diff --git a/configure.ac b/configure.ac
index 339ee3b2f2..43e517f370 100644
--- a/configure.ac
+++ b/configure.ac
@@ -526,6 +526,7 @@ AS_CASE(["$target_os"],
 	RT_VER=`echo "$rb_cv_msvcrt" | tr -cd [0-9]`
 	test "$RT_VER" = "" && RT_VER=60
 	test "$rb_cv_msvcrt" = "ucrt" && RT_VER=140
+	AS_IF([test $RT_VER -lt 80], AC_MSG_ERROR(Runtime library $RT_VER is not supported))
 	AC_DEFINE_UNQUOTED(RUBY_MSVCRT_VERSION, $RT_VER)
 	sysconfdir=
     ])
diff --git a/debug.c b/debug.c
index 4717a0bc9c..b92faa8f36 100644
--- a/debug.c
+++ b/debug.c
@@ -168,9 +168,7 @@ ruby_debug_breakpoint(void)
 }
 
 #if defined _WIN32
-# if RUBY_MSVCRT_VERSION >= 80
 extern int ruby_w32_rtc_error;
-# endif
 #endif
 #if defined _WIN32 || defined __CYGWIN__
 #include <windows.h>
@@ -233,9 +231,7 @@ ruby_env_debug_option(const char *str, int len, void *arg)
     SET_WHEN("ci", ruby_on_ci, 1);
     SET_WHEN_UINT("rgengc", &ruby_rgengc_debug, 1, ruby_rgengc_debug = 1);
 #if defined _WIN32
-# if RUBY_MSVCRT_VERSION >= 80
     SET_WHEN("rtc_error", ruby_w32_rtc_error, 1);
-# endif
 #endif
 #if defined _WIN32 || defined __CYGWIN__
     SET_WHEN_UINT("codepage", ruby_w32_codepage, numberof(ruby_w32_codepage),
diff --git a/error.c b/error.c
index abf50b696a..f452f7b01c 100644
--- a/error.c
+++ b/error.c
@@ -1076,7 +1076,7 @@ NORETURN(static void die(void));
 static void
 die(void)
 {
-#if defined(_WIN32) && defined(RUBY_MSVCRT_VERSION) && RUBY_MSVCRT_VERSION >= 80
+#if defined(_WIN32)
     _set_abort_behavior( 0, _CALL_REPORTFAULT);
 #endif
 
diff --git a/ext/socket/getaddrinfo.c b/ext/socket/getaddrinfo.c
index 5b82499655..9a65490b1d 100644
--- a/ext/socket/getaddrinfo.c
+++ b/ext/socket/getaddrinfo.c
@@ -62,9 +62,6 @@
 #endif
 #include <unistd.h>
 #else
-#if defined(_MSC_VER) && _MSC_VER <= 1200
-#include <windows.h>
-#endif
 #include <winsock2.h>
 #include <ws2tcpip.h>
 #include <io.h>
diff --git a/ext/socket/getnameinfo.c b/ext/socket/getnameinfo.c
index ffda7f98c7..98da8c1647 100644
--- a/ext/socket/getnameinfo.c
+++ b/ext/socket/getnameinfo.c
@@ -55,9 +55,6 @@
 #endif
 #endif
 #ifdef _WIN32
-#if defined(_MSC_VER) && _MSC_VER <= 1200
-#include <windows.h>
-#endif
 #include <winsock2.h>
 #include <ws2tcpip.h>
 #define snprintf _snprintf
diff --git a/include/ruby/internal/compiler_is/msvc.h b/include/ruby/internal/compiler_is/msvc.h
index 8a864ea558..824f0ecc21 100644
--- a/include/ruby/internal/compiler_is/msvc.h
+++ b/include/ruby/internal/compiler_is/msvc.h
@@ -38,19 +38,8 @@
 # define RBIMPL_COMPILER_VERSION_MINOR (_MSC_FULL_VER % 10000000 / 100000)
 # define RBIMPL_COMPILER_VERSION_PATCH (_MSC_FULL_VER            % 100000)
 
-#elif defined(_MSC_FULL_VER)
-# define RBIMPL_COMPILER_IS_MSVC 1
-# /* _MSC_FULL_VER = XXYYZZZZ */
-# define RBIMPL_COMPILER_VERSION_MAJOR (_MSC_FULL_VER / 1000000)
-# define RBIMPL_COMPILER_VERSION_MINOR (_MSC_FULL_VER % 1000000 / 10000)
-# define RBIMPL_COMPILER_VERSION_PATCH (_MSC_FULL_VER           % 10000)
-
 #else
-# define RBIMPL_COMPILER_IS_MSVC 1
-# /* _MSC_VER = XXYY */
-# define RBIMPL_COMPILER_VERSION_MAJOR (_MSC_VER / 100)
-# define RBIMPL_COMPILER_VERSION_MINOR (_MSC_VER % 100)
-# define RBIMPL_COMPILER_VERSION_PATCH 0
+# error Unsupported MSVC version
 #endif
 
 #endif /* RBIMPL_COMPILER_IS_MSVC_H */
diff --git a/include/ruby/win32.h b/include/ruby/win32.h
index 69e92ed9ff..57e8ab471b 100644
--- a/include/ruby/win32.h
+++ b/include/ruby/win32.h
@@ -30,15 +30,10 @@ extern "C++" {			/* template without extern "C++" */
 #if !defined(_WIN64) && !defined(WIN32)
 #define WIN32
 #endif
-#if defined(_MSC_VER) && _MSC_VER <= 1200
-#include <windows.h>
-#endif
 #include <winsock2.h>
 #include <ws2tcpip.h>
 #include <mswsock.h>
-#if !defined(_MSC_VER) || _MSC_VER >= 1400
 #include <iphlpapi.h>
-#endif
 #if defined(__cplusplus) && defined(_MSC_VER)
 }
 #endif
@@ -59,13 +54,7 @@ extern "C++" {			/* template without extern "C++" */
 #include <direct.h>
 #include <process.h>
 #include <time.h>
-#if defined(__cplusplus) && defined(_MSC_VER) && _MSC_VER == 1200
-extern "C++" {			/* template without extern "C++" */
-#endif
 #include <math.h>
-#if defined(__cplusplus) && defined(_MSC_VER) && _MSC_VER == 1200
-}
-#endif
 #include <signal.h>
 #include <sys/stat.h>
 #include <sys/types.h>
@@ -436,7 +425,7 @@ extern int rb_w32_utruncate(const char *path, rb_off_t length);
 #define HAVE_TRUNCATE 1
 #define truncate rb_w32_utruncate
 
-#if defined(_MSC_VER) && _MSC_VER >= 1400 && _MSC_VER < 1800
+#if defined(_MSC_VER) && _MSC_VER < 1800
 #define strtoll  _strtoi64
 #define strtoull _strtoui64
 #endif
diff --git a/internal/bits.h b/internal/bits.h
index 2b5aecf112..bbd59ffaca 100644
--- a/internal/bits.h
+++ b/internal/bits.h
@@ -30,13 +30,13 @@
 #include <stdint.h>             /* for uintptr_t */
 #include "internal/compilers.h" /* for MSC_VERSION_SINCE */
 
-#if MSC_VERSION_SINCE(1310)
+#ifdef _MSC_VER
 # include <stdlib.h>            /* for _byteswap_uint64 */
 #endif
 
 #if defined(HAVE_X86INTRIN_H)
 # include <x86intrin.h>         /* for _lzcnt_u64 */
-#elif MSC_VERSION_SINCE(1310)
+#elif defined(_MSC_VER)
 # include <intrin.h>            /* for the following intrinsics */
 #endif
 
@@ -50,16 +50,13 @@
 # pragma intrinsic(__lzcnt64)
 #endif
 
-#if MSC_VERSION_SINCE(1310)
+#if defined(_MSC_VER)
 # pragma intrinsic(_rotl)
 # pragma intrinsic(_rotr)
 # ifdef _WIN64
 #  pragma intrinsic(_rotl64)
 #  pragma intrinsic(_rotr64)
 # endif
-#endif
-
-#if MSC_VERSION_SINCE(1400)
 # pragma intrinsic(_BitScanForward)
 # pragma intrinsic(_BitScanReverse)
 # ifdef _WIN64
@@ -266,7 +263,7 @@ ruby_swap16(uint16_t x)
 #if __has_builtin(__builtin_bswap16)
     return __builtin_bswap16(x);
 
-#elif MSC_VERSION_SINCE(1310)
+#elif defined(_MSC_VER)
     return _byteswap_ushort(x);
 
 #else
@@ -281,7 +278,7 @@ ruby_swap32(uint32_t x)
 #if __has_builtin(__builtin_bswap32)
     return __builtin_bswap32(x);
 
-#elif MSC_VERSION_SINCE(1310)
+#elif defined(_MSC_VER)
     return _byteswap_ulong(x);
 
 #else
@@ -298,7 +295,7 @@ ruby_swap64(uint64_t x)
 #if __has_builtin(__builtin_bswap64)
     return __builtin_bswap64(x);
 
-#elif MSC_VERSION_SINCE(1310)
+#elif defined(_MSC_VER)
     return _byteswap_uint64(x);
 
 #else
@@ -323,7 +320,7 @@ nlz_int32(uint32_t x)
 #elif defined(__x86_64__) && defined(__LZCNT__)
     return (unsigned int)_lzcnt_u32(x);
 
-#elif MSC_VERSION_SINCE(1400) /* &&! defined(__AVX2__) */
+#elif defined(_MSC_VER) /* &&! defined(__AVX2__) */
     unsigned long r;
     return _BitScanReverse(&r, x) ? (31 - (int)r) : 32;
 
@@ -352,7 +349,7 @@ nlz_int64(uint64_t x)
 #elif defined(__x86_64__) && defined(__LZCNT__)
     return (unsigned int)_lzcnt_u64(x);
 
-#elif defined(_WIN64) && MSC_VERSION_SINCE(1400) /* &&! defined(__AVX2__) */
+#elif defined(_WIN64) && defined(_MSC_VER) /* &&! defined(__AVX2__) */
     unsigned long r;
     return _BitScanReverse64(&r, x) ? (63u - (unsigned int)r) : 64;
 
@@ -538,7 +535,7 @@ ntz_int32(uint32_t x)
 #if defined(__x86_64__) && defined(__BMI__)
     return (unsigned)_tzcnt_u32(x);
 
-#elif MSC_VERSION_SINCE(1400)
+#elif defined(_MSC_VER)
     /* :FIXME: Is there any way to issue TZCNT instead of BSF, apart from using
      *         assembly?  Because issuing LZCNT seems possible (see nlz.h). */
     unsigned long r;
@@ -559,8 +556,8 @@ ntz_int64(uint64_t x)
 {
 #if defined(__x86_64__) && defined(__BMI__)
     return (unsigned)_tzcnt_u64(x);
-
-#elif defined(_WIN64) && MSC_VERSION_SINCE(1400)
+`
+#elif defined(_WIN64) && defined(_MSC_VER)
     unsigned long r;
     return _BitScanForward64(&r, x) ? (int)r : 64;
 
@@ -608,10 +605,10 @@ RUBY_BIT_ROTL(VALUE v, int n)
 #elif __has_builtin(__builtin_rotateleft64) && (SIZEOF_VALUE * CHAR_BIT == 64)
     return __builtin_rotateleft64(v, n);
 
-#elif MSC_VERSION_SINCE(1310) && (SIZEOF_VALUE * CHAR_BIT == 32)
+#elif defined(_MSC_VER) && (SIZEOF_VALUE * CHAR_BIT == 32)
     return _rotl(v, n);
 
-#elif MSC_VERSION_SINCE(1310) && (SIZEOF_VALUE * CHAR_BIT == 64)
+#elif defined(_MSC_VER) && (SIZEOF_VALUE * CHAR_BIT == 64)
     return _rotl64(v, n);
 
 #elif defined(_lrotl) && (SIZEOF_VALUE == SIZEOF_LONG)
@@ -632,10 +629,10 @@ RUBY_BIT_ROTR(VALUE v, int n)
 #elif __has_builtin(__builtin_rotateright64) && (SIZEOF_VALUE * CHAR_BIT == 64)
     return __builtin_rotateright64(v, n);
 
-#elif MSC_VERSION_SINCE(1310) && (SIZEOF_VALUE * CHAR_BIT == 32)
+#elif defined(_MSC_VER) && (SIZEOF_VALUE * CHAR_BIT == 32)
     return _rotr(v, n);
 
-#elif MSC_VERSION_SINCE(1310) && (SIZEOF_VALUE * CHAR_BIT == 64)
+#elif defined(_MSC_VER) && (SIZEOF_VALUE * CHAR_BIT == 64)
     return _rotr64(v, n);
 
 #elif defined(_lrotr) && (SIZEOF_VALUE == SIZEOF_LONG)
diff --git a/numeric.c b/numeric.c
index 731a809523..3d6648f7d6 100644
--- a/numeric.c
+++ b/numeric.c
@@ -1591,17 +1591,11 @@ rb_float_equal(VALUE x, VALUE y)
     }
     else if (RB_FLOAT_TYPE_P(y)) {
         b = RFLOAT_VALUE(y);
-#if MSC_VERSION_BEFORE(1300)
-        if (isnan(b)) return Qfalse;
-#endif
     }
     else {
         return num_equal(x, y);
     }
     a = RFLOAT_VALUE(x);
-#if MSC_VERSION_BEFORE(1300)
-    if (isnan(a)) return Qfalse;
-#endif
     return RBOOL(a == b);
 }
 
@@ -1734,16 +1728,10 @@ rb_float_gt(VALUE x, VALUE y)
     }
     else if (RB_FLOAT_TYPE_P(y)) {
         b = RFLOAT_VALUE(y);
-#if MSC_VERSION_BEFORE(1300)
-        if (isnan(b)) return Qfalse;
-#endif
     }
     else {
         return rb_num_coerce_relop(x, y, '>');
     }
-#if MSC_VERSION_BEFORE(1300)
-    if (isnan(a)) return Qfalse;
-#endif
     return RBOOL(a > b);
 }
 
@@ -1777,16 +1765,10 @@ flo_ge(VALUE x, VALUE y)
     }
     else if (RB_FLOAT_TYPE_P(y)) {
         b = RFLOAT_VALUE(y);
-#if MSC_VERSION_BEFORE(1300)
-        if (isnan(b)) return Qfalse;
-#endif
     }
     else {
         return rb_num_coerce_relop(x, y, idGE);
     }
-#if MSC_VERSION_BEFORE(1300)
-    if (isnan(a)) return Qfalse;
-#endif
     return RBOOL(a >= b);
 }
 
@@ -1819,16 +1801,10 @@ flo_lt(VALUE x, VALUE y)
     }
     else if (RB_FLOAT_TYPE_P(y)) {
         b = RFLOAT_VALUE(y);
-#if MSC_VERSION_BEFORE(1300)
-        if (isnan(b)) return Qfalse;
-#endif
     }
     else {
         return rb_num_coerce_relop(x, y, '<');
     }
-#if MSC_VERSION_BEFORE(1300)
-    if (isnan(a)) return Qfalse;
-#endif
     return RBOOL(a < b);
 }
 
@@ -1862,16 +1838,10 @@ flo_le(VALUE x, VALUE y)
     }
     else if (RB_FLOAT_TYPE_P(y)) {
         b = RFLOAT_VALUE(y);
-#if MSC_VERSION_BEFORE(1300)
-        if (isnan(b)) return Qfalse;
-#endif
     }
     else {
         return rb_num_coerce_relop(x, y, idLE);
     }
-#if MSC_VERSION_BEFORE(1300)
-    if (isnan(a)) return Qfalse;
-#endif
     return RBOOL(a <= b);
 }
 
@@ -1899,10 +1869,7 @@ rb_float_eql(VALUE x, VALUE y)
     if (RB_FLOAT_TYPE_P(y)) {
         double a = RFLOAT_VALUE(x);
         double b = RFLOAT_VALUE(y);
-#if MSC_VERSION_BEFORE(1300)
-        if (isnan(a) || isnan(b)) return Qfalse;
-#endif
-    return RBOOL(a == b);
+        return RBOOL(a == b);
     }
     return Qfalse;
 }
diff --git a/parser_bits.h b/parser_bits.h
index ca7535280e..cbe42db396 100644
--- a/parser_bits.h
+++ b/parser_bits.h
@@ -30,13 +30,13 @@
 #include <stdint.h>             /* for uintptr_t */
 #include "internal/compilers.h" /* for MSC_VERSION_SINCE */
 
-#if MSC_VERSION_SINCE(1310)
+#if defined(_MSC_VER)
 # include <stdlib.h>            /* for _byteswap_uint64 */
 #endif
 
 #if defined(HAVE_X86INTRIN_H)
 # include <x86intrin.h>         /* for _lzcnt_u64 */
-#elif MSC_VERSION_SINCE(1310)
+#elif defined(_MSC_VER)
 # include <intrin.h>            /* for the following intrinsics */
 #endif
 
@@ -50,7 +50,7 @@
 # pragma intrinsic(__lzcnt64)
 #endif
 
-#if MSC_VERSION_SINCE(1310)
+#if defined(_MSC_VER)
 # pragma intrinsic(_rotl)
 # pragma intrinsic(_rotr)
 # ifdef _WIN64
@@ -59,7 +59,7 @@
 # endif
 #endif
 
-#if MSC_VERSION_SINCE(1400)
+#if defined(_MSC_VER)
 # pragma intrinsic(_BitScanForward)
 # pragma intrinsic(_BitScanReverse)
 # ifdef _WIN64
@@ -180,7 +180,7 @@ ruby_swap16(uint16_t x)
 #if __has_builtin(__builtin_bswap16)
     return __builtin_bswap16(x);
 
-#elif MSC_VERSION_SINCE(1310)
+#elif defined(_MSC_VER)
     return _byteswap_ushort(x);
 
 #else
@@ -195,7 +195,7 @@ ruby_swap32(uint32_t x)
 #if __has_builtin(__builtin_bswap32)
     return __builtin_bswap32(x);
 
-#elif MSC_VERSION_SINCE(1310)
+#elif defined(_MSC_VER)
     return _byteswap_ulong(x);
 
 #else
@@ -212,7 +212,7 @@ ruby_swap64(uint64_t x)
 #if __has_builtin(__builtin_bswap64)
     return __builtin_bswap64(x);
 
-#elif MSC_VERSION_SINCE(1310)
+#elif defined(_MSC_VER)
     return _byteswap_uint64(x);
 
 #else
@@ -237,7 +237,7 @@ nlz_int32(uint32_t x)
 #elif defined(__x86_64__) && defined(__LZCNT__)
     return (unsigned int)_lzcnt_u32(x);
 
-#elif MSC_VERSION_SINCE(1400) /* &&! defined(__AVX2__) */
+#elif defined(_MSC_VER) /* &&! defined(__AVX2__) */
     unsigned long r;
     return _BitScanReverse(&r, x) ? (31 - (int)r) : 32;
 
@@ -266,7 +266,7 @@ nlz_int64(uint64_t x)
 #elif defined(__x86_64__) && defined(__LZCNT__)
     return (unsigned int)_lzcnt_u64(x);
 
-#elif defined(_WIN64) && MSC_VERSION_SINCE(1400) /* &&! defined(__AVX2__) */
+#elif defined(_WIN64) && defined(_MSC_VER) /* &&! defined(__AVX2__) */
     unsigned long r;
     return _BitScanReverse64(&r, x) ? (63u - (unsigned int)r) : 64;
 
@@ -452,7 +452,7 @@ ntz_int32(uint32_t x)
 #if defined(__x86_64__) && defined(__BMI__)
     return (unsigned)_tzcnt_u32(x);
 
-#elif MSC_VERSION_SINCE(1400)
+#elif defined(_MSC_VER)
     /* :FIXME: Is there any way to issue TZCNT instead of BSF, apart from using
      *         assembly?  Because issuing LZCNT seems possible (see nlz.h). */
     unsigned long r;
@@ -474,7 +474,7 @@ ntz_int64(uint64_t x)
 #if defined(__x86_64__) && defined(__BMI__)
     return (unsigned)_tzcnt_u64(x);
 
-#elif defined(_WIN64) && MSC_VERSION_SINCE(1400)
+#elif defined(_WIN64) && defined(_MSC_VER)
     unsigned long r;
     return _BitScanForward64(&r, x) ? (int)r : 64;
 
@@ -522,10 +522,10 @@ RUBY_BIT_ROTL(VALUE v, int n)
 #elif __has_builtin(__builtin_rotateleft64) && (SIZEOF_VALUE * CHAR_BIT == 64)
     return __builtin_rotateleft64(v, n);
 
-#elif MSC_VERSION_SINCE(1310) && (SIZEOF_VALUE * CHAR_BIT == 32)
+#elif defined(_MSC_VER) && (SIZEOF_VALUE * CHAR_BIT == 32)
     return _rotl(v, n);
 
-#elif MSC_VERSION_SINCE(1310) && (SIZEOF_VALUE * CHAR_BIT == 64)
+#elif defined(_MSC_VER) && (SIZEOF_VALUE * CHAR_BIT == 64)
     return _rotl64(v, n);
 
 #elif defined(_lrotl) && (SIZEOF_VALUE == SIZEOF_LONG)
@@ -546,10 +546,10 @@ RUBY_BIT_ROTR(VALUE v, int n)
 #elif __has_builtin(__builtin_rotateright64) && (SIZEOF_VALUE * CHAR_BIT == 64)
     return __builtin_rotateright64(v, n);
 
-#elif MSC_VERSION_SINCE(1310) && (SIZEOF_VALUE * CHAR_BIT == 32)
+#elif defined(_MSC_VER) && (SIZEOF_VALUE * CHAR_BIT == 32)
     return _rotr(v, n);
 
-#elif MSC_VERSION_SINCE(1310) && (SIZEOF_VALUE * CHAR_BIT == 64)
+#elif defined(_MSC_VER) && (SIZEOF_VALUE * CHAR_BIT == 64)
     return _rotr64(v, n);
 
 #elif defined(_lrotr) && (SIZEOF_VALUE == SIZEOF_LONG)
diff --git a/random.c b/random.c
index bf5588186c..0fd953b81e 100644
--- a/random.c
+++ b/random.c
@@ -230,7 +230,7 @@ int_pair_to_real_inclusive(uint32_t a, uint32_t b)
     const uint128_t m = ((uint128_t)1 << dig) | 1;
     uint128_t x = ((uint128_t)a << 32) | b;
     r = (double)(uint64_t)((x * m) >> 64);
-#elif defined HAVE_UINT64_T && !MSC_VERSION_BEFORE(1300)
+#elif defined HAVE_UINT64_T
     uint64_t x = ((uint64_t)a << dig_u) +
         (((uint64_t)b + (a >> dig_u)) >> dig_r64);
     r = (double)x;
diff --git a/regint.h b/regint.h
index 9924e5f62a..9f59ca6006 100644
--- a/regint.h
+++ b/regint.h
@@ -266,19 +266,6 @@
 # include <stdio.h>
 #endif
 
-#ifdef _WIN32
-# if defined(_MSC_VER) && (_MSC_VER < 1300)
-#  ifndef _INTPTR_T_DEFINED
-#   define _INTPTR_T_DEFINED
-typedef int intptr_t;
-#  endif
-#  ifndef _UINTPTR_T_DEFINED
-#   define _UINTPTR_T_DEFINED
-typedef unsigned int uintptr_t;
-#  endif
-# endif
-#endif /* _WIN32 */
-
 #ifndef PRIdPTR
 # ifdef _WIN64
 #  define PRIdPTR	"I64d"
diff --git a/vm_insnhelper.c b/vm_insnhelper.c
index 1b1eeb69d9..8495ee59ef 100644
--- a/vm_insnhelper.c
+++ b/vm_insnhelper.c
@@ -2518,15 +2518,6 @@ opt_equality_specialized(VALUE recv, VALUE obj)
         double a = RFLOAT_VALUE(recv);
         double b = RFLOAT_VALUE(obj);
 
-#if MSC_VERSION_BEFORE(1300)
-        if (isnan(a)) {
-            return Qfalse;
-        }
-        else if (isnan(b)) {
-            return Qfalse;
-        }
-        else
-#endif
         return RBOOL(a == b);
     }
     else if (RBASIC_CLASS(recv) == rb_cString && EQ_UNREDEFINED_P(STRING)) {
@@ -2624,37 +2615,27 @@ check_match(rb_execution_context_t *ec, VALUE pattern, VALUE target, enum vm_che
 }
 
 
-#if MSC_VERSION_BEFORE(1300)
-#define CHECK_CMP_NAN(a, b) if (isnan(a) || isnan(b)) return Qfalse;
-#else
-#define CHECK_CMP_NAN(a, b) /* do nothing */
-#endif
-
 static inline VALUE
 double_cmp_lt(double a, double b)
 {
-    CHECK_CMP_NAN(a, b);
     return RBOOL(a < b);
 }
 
 static inline VALUE
 double_cmp_le(double a, double b)
 {
-    CHECK_CMP_NAN(a, b);
     return RBOOL(a <= b);
 }
 
 static inline VALUE
 double_cmp_gt(double a, double b)
 {
-    CHECK_CMP_NAN(a, b);
     return RBOOL(a > b);
 }
 
 static inline VALUE
 double_cmp_ge(double a, double b)
 {
-    CHECK_CMP_NAN(a, b);
     return RBOOL(a >= b);
 }
 
@@ -6878,7 +6859,6 @@ vm_opt_lt(VALUE recv, VALUE obj)
     else if (RBASIC_CLASS(recv) == rb_cFloat &&
              RBASIC_CLASS(obj)  == rb_cFloat &&
              BASIC_OP_UNREDEFINED_P(BOP_LT, FLOAT_REDEFINED_OP_FLAG)) {
-        CHECK_CMP_NAN(RFLOAT_VALUE(recv), RFLOAT_VALUE(obj));
         return RBOOL(RFLOAT_VALUE(recv) < RFLOAT_VALUE(obj));
     }
     else {
@@ -6903,7 +6883,6 @@ vm_opt_le(VALUE recv, VALUE obj)
     else if (RBASIC_CLASS(recv) == rb_cFloat &&
              RBASIC_CLASS(obj)  == rb_cFloat &&
              BASIC_OP_UNREDEFINED_P(BOP_LE, FLOAT_REDEFINED_OP_FLAG)) {
-        CHECK_CMP_NAN(RFLOAT_VALUE(recv), RFLOAT_VALUE(obj));
         return RBOOL(RFLOAT_VALUE(recv) <= RFLOAT_VALUE(obj));
     }
     else {
@@ -6928,7 +6907,6 @@ vm_opt_gt(VALUE recv, VALUE obj)
     else if (RBASIC_CLASS(recv) == rb_cFloat &&
              RBASIC_CLASS(obj)  == rb_cFloat &&
              BASIC_OP_UNREDEFINED_P(BOP_GT, FLOAT_REDEFINED_OP_FLAG)) {
-        CHECK_CMP_NAN(RFLOAT_VALUE(recv), RFLOAT_VALUE(obj));
         return RBOOL(RFLOAT_VALUE(recv) > RFLOAT_VALUE(obj));
     }
     else {
@@ -6953,7 +6931,6 @@ vm_opt_ge(VALUE recv, VALUE obj)
     else if (RBASIC_CLASS(recv) == rb_cFloat &&
              RBASIC_CLASS(obj)  == rb_cFloat &&
              BASIC_OP_UNREDEFINED_P(BOP_GE, FLOAT_REDEFINED_OP_FLAG)) {
-        CHECK_CMP_NAN(RFLOAT_VALUE(recv), RFLOAT_VALUE(obj));
         return RBOOL(RFLOAT_VALUE(recv) >= RFLOAT_VALUE(obj));
     }
     else {
diff --git a/win32/Makefile.sub b/win32/Makefile.sub
index 81a33277af..5bad1d3d75 100644
--- a/win32/Makefile.sub
+++ b/win32/Makefile.sub
@@ -130,6 +130,11 @@ TEST_RUNNABLE = yes
 
 CAT_DEPEND = type
 
+!if !defined(MSC_VER)
+! error MSC_VER not defined.  Retry from configure pass.
+!else if $(MSC_VER) < 1400
+! error MSVC $(MSC_VER) is not supported
+!endif
 !if !defined(MACHINE)
 MACHINE = x86
 !endif
@@ -140,9 +145,6 @@ PROCESSOR_LEVEL = 5
 !if 6 < $(PROCESSOR_LEVEL)
 PROCESSOR_LEVEL = 6
 !endif
-!if $(MSC_VER) < 1400
-PROCESSOR_FLAG = -G$(PROCESSOR_LEVEL)
-!endif
 CPU = i$(PROCESSOR_LEVEL)86
 ARCH = i386
 !else
@@ -159,12 +161,8 @@ XCFLAGS = $(XCFLAGS) -DRUBY_DEVEL=1
 XCFLAGS = $(XCFLAGS) -Dmodular_gc_dir="$(modular_gc_dir)"
 !endif
 !if !defined(OPTFLAGS)
-!if $(MSC_VER) < 1400
-OPTFLAGS = -O2b2xg-
-!else
 OPTFLAGS = -O2sy-
 !endif
-!endif
 !if $(MSC_VER) >= 1900
 OPTFLAGS = $(OPTFLAGS) -Zc:inline
 !endif
@@ -176,6 +174,8 @@ PLATFORM = mswin32
 !endif
 !if !defined(RT)
 !error RT not defined.  Retry from configure pass.
+!else if $(RT_VER) < 80
+! error Runtime library $(RT_VER) is not supported
 !endif
 !ifndef NTVER
 NTVER = _WIN32_WINNT_WIN8
@@ -278,13 +278,9 @@ RUNTIMEFLAG   = -MD
 COMPILERFLAG  = -Zm600
 !endif
 !if !defined(WARNFLAGS)
-!if $(MSC_VER) >= 1400
 WARNFLAGS = -W2 -wd4100 -wd4127 -wd4210 -wd4214 -wd4255 -wd4574 \
 	    -wd4668 -wd4710 -wd4711 -wd4820 -wd4996 \
 	    -we4028 -we4142 -we4047 -we4013
-!else
-WARNFLAGS = -W2
-!endif
 !if $(MSC_VER) >= 1944
 # https://developercommunity.visualstudio.com/t/warning-C5287:-operands-are-different-e/10877942
 WARNFLAGS = $(WARNFLAGS) -wd5287
@@ -318,9 +314,7 @@ EXTSOLIBS =
 !endif
 !if !defined(LIBS)
 LIBS = user32.lib advapi32.lib shell32.lib ws2_32.lib
-!if $(MSC_VER) >= 1400
 LIBS = $(LIBS) iphlpapi.lib
-!endif
 !if defined(USE_GMP)
 LIBS = $(LIBS) gmp.lib
 !endif
@@ -697,11 +691,7 @@ $(CONFIG_H): $(MKFILES) $(srcdir)/win32/Makefile.sub $(win_srcdir)/Makefile.sub
 !if $(MSC_VER) >= 1920
 #define HAVE_AFUNIX_H 1
 !endif
-!if $(MSC_VER) >= 1400
 #define HAVE_LONG_LONG 1
-!else
-#define ULL_TO_DOUBLE(n) ((double)(unsigned long)((n)>>32) * (1I64 << 32) + (unsigned long)(n))
-!endif
 #define HAVE_OFF_T 1
 #define rb_off_t __int64
 #define SIGNEDNESS_OF_OFF_T -1
@@ -710,11 +700,7 @@ $(CONFIG_H): $(MKFILES) $(srcdir)/win32/Makefile.sub $(win_srcdir)/Makefile.sub
 #define SIZEOF_INT 4
 #define SIZEOF_SHORT 2
 #define SIZEOF_LONG 4
-!if $(MSC_VER) >= 1400
 #define SIZEOF_LONG_LONG 8
-!else
-#define SIZEOF_LONG_LONG 0
-!endif
 #define SIZEOF___INT64 8
 #ifndef _INTEGRAL_MAX_BITS
 #define _INTEGRAL_MAX_BITS 64
@@ -729,15 +715,9 @@ $(CONFIG_H): $(MKFILES) $(srcdir)/win32/Makefile.sub $(win_srcdir)/Makefile.sub
 #define SIZEOF_DOUBLE 8
 #define SIGNEDNESS_OF_TIME_T -1
 #define NEGATIVE_TIME_T 1
-!if $(RT_VER) >= 80
 #define SIZEOF_TIME_T 8
 #define TIMET2NUM(v) LL2NUM(v)
 #define NUM2TIMET(v) NUM2LL(v)
-!else
-#define SIZEOF_TIME_T 4
-#define TIMET2NUM(v) LONG2NUM(v)
-#define NUM2TIMET(v) NUM2LONG(v)
-!endif
 #define CLOCKID2NUM(v) INT2NUM(v)
 #define NUM2CLOCKID(v) NUM2INT(v)
 #define SIZEOF_CLOCK_T 4
@@ -753,22 +733,15 @@ $(CONFIG_H): $(MKFILES) $(srcdir)/win32/Makefile.sub $(win_srcdir)/Makefile.sub
 #define SIZEOF_INTPTR_T 4
 #define SIZEOF_UINTPTR_T 4
 !endif
-!if $(MSC_VER) < 1400
-#define SIZE_MAX UINT_MAX
-!endif
 !if $(MSC_VER) >= 1800
 #define HAVE_VA_COPY 1
 !else
 #define HAVE_VA_COPY_VIA_STRUCT_ASSIGNMENT 1
 !endif
-!if $(MSC_VER) > 1100
 #define NORETURN(x) __declspec(noreturn) x
-!endif
-!if $(MSC_VER) >= 1300
 #define DEPRECATED(x) __declspec(deprecated) x
 #define RUBY_CXX_DEPRECATED(mesg) __declspec(deprecated(mesg))
 #define NOINLINE(x) __declspec(noinline) x
-!endif
 #define ALWAYS_INLINE(x) __forceinline x
 #define WARN_UNUSED_RESULT(x) x
 #define MAYBE_UNUSED(x) x
@@ -1119,7 +1092,7 @@ s,@LIBPATHFLAG@,-libpath:%s,;t t
 s,@RPATHFLAG@,,;t t
 s,@LIBARG@,%s.lib,;t t
 s,@LINK_SO@,$$(LDSHARED) -Fe$$(@) $$(OBJS) $$(LIBS) $$(LOCAL_LIBS) -link $$(DLDFLAGS) -implib:$$(*F:.so=)-$$(arch).lib -pdb:$$(*F:.so=)-$$(arch).pdb -def:$$(DEFFILE),;t t
-!if $(MSC_VER) >= 1400 && $(MSC_VER) < 1800
+!if $(MSC_VER) < 1800
 s,@LINK_SO@,@if exist $$(@).manifest $$(RUBY) -run -e wait_writable -- -n 10 $$(@),;t t
 s,@LINK_SO@,@if exist $$(@).manifest $(MANIFESTTOOL) -manifest $$(@).manifest -outputresource:$$(@);2,;t t
 s,@LINK_SO@,@if exist $$(@).manifest $$(RM) $$(@:/=\).manifest,;t t
diff --git a/win32/file.c b/win32/file.c
index f137f04c43..26b99715cd 100644
--- a/win32/file.c
+++ b/win32/file.c
@@ -629,14 +629,10 @@ rb_freopen(VALUE fname, const char *mode, FILE *file)
     len = MultiByteToWideChar(CP_UTF8, 0, name, n, wname, len);
     wname[len] = L'\0';
     RB_GC_GUARD(fname);
-#if RUBY_MSVCRT_VERSION < 80 && !defined(HAVE__WFREOPEN_S)
-    e = _wfreopen(wname, wmode, file) ? 0 : errno;
-#else
     {
         FILE *newfp = 0;
         e = _wfreopen_s(&newfp, wname, wmode, file);
     }
-#endif
     ALLOCV_END(wtmp);
     return e;
 }
diff --git a/win32/win32.c b/win32/win32.c
index e7dfe2b065..9cffd67597 100644
--- a/win32/win32.c
+++ b/win32/win32.c
@@ -21,6 +21,10 @@
 
 #undef __STRICT_ANSI__
 
+/* Visual C++ 2005 (8.0):
+ * - _MSC_VER: 1400
+ * - MSVCRT_VERSION: 80
+ */
 #include "ruby/ruby.h"
 #include "ruby/encoding.h"
 #include "ruby/io.h"
@@ -42,7 +46,7 @@
 #include <shlobj.h>
 #include <mbstring.h>
 #include <shlwapi.h>
-#if defined _MSC_VER && _MSC_VER >= 1400
+#if defined _MSC_VER
 #include <crtdbg.h>
 #include <rtcapi.h>
 #endif
@@ -65,10 +69,6 @@
 #include "encindex.h"
 #define isdirsep(x) ((x) == '/' || (x) == '\\')
 
-#if defined _MSC_VER && _MSC_VER <= 1200
-# define CharNextExA(cp, p, flags) CharNextExA((WORD)(cp), (p), (flags))
-#endif
-
 static int w32_wopen(const WCHAR *file, int oflag, int perm);
 static int w32_stati128(const char *path, struct stati128 *st, UINT cp, BOOL lstat);
 static char *w32_getenv(const char *name, UINT cp);
@@ -503,11 +503,6 @@ rb_w32_special_folder(int type)
     return rb_w32_conv_from_wchar(path, rb_filesystem_encoding());
 }
 
-#if defined _MSC_VER && _MSC_VER <= 1200
-/* License: Ruby's */
-#define GetSystemWindowsDirectoryW GetWindowsDirectoryW
-#endif
-
 /* License: Ruby's */
 UINT
 rb_w32_system_tmpdir(WCHAR *path, UINT len)
@@ -629,7 +624,6 @@ init_env(void)
 
 static void init_stdhandle(void);
 
-#if RUBY_MSVCRT_VERSION >= 80
 /* License: Ruby's */
 static void
 invalid_parameter(const wchar_t *expr, const wchar_t *func, const wchar_t *file, unsigned int line, uintptr_t dummy)
@@ -639,7 +633,7 @@ invalid_parameter(const wchar_t *expr, const wchar_t *func, const wchar_t *file,
 
 int ruby_w32_rtc_error;
 
-# ifndef __MINGW32__
+#ifndef __MINGW32__
 /* License: Ruby's */
 RBIMPL_ATTR_NONNULL((5))
 RBIMPL_ATTR_FORMAT(RBIMPL_PRINTF_FORMAT, 5, 6)
@@ -658,7 +652,6 @@ rtc_error_handler(int e, const char *src, int line, const char *exe, const char
     rb_write_error2(RSTRING_PTR(str), RSTRING_LEN(str));
     return 0;
 }
-# endif
 #endif
 
 static CRITICAL_SECTION select_mutex;
@@ -852,13 +845,11 @@ socklist_delete(SOCKET *sockp, int *flagp)
     return ret;
 }
 
-#if RUBY_MSVCRT_VERSION >= 80
 # ifdef __MINGW32__
 #  define _CrtSetReportMode(type,mode) ((void)0)
 #  define _RTC_SetErrorFunc(func) ((void)0)
 # endif
 static void set_pioinfo_extra(void);
-#endif
 static int w32_cmdvector(const WCHAR *, char ***, UINT, rb_encoding *);
 //
 // Initialization stuff
@@ -867,13 +858,10 @@ static int w32_cmdvector(const WCHAR *, char ***, UINT, rb_encoding *);
 void
 rb_w32_sysinit(int *argc, char ***argv)
 {
-#if RUBY_MSVCRT_VERSION >= 80
-
     _CrtSetReportMode(_CRT_ASSERT, 0);
     _set_invalid_parameter_handler(invalid_parameter);
     _RTC_SetErrorFunc(rtc_error_handler);
     set_pioinfo_extra();
-#endif
     SetErrorMode(SEM_FAILCRITICALERRORS|SEM_NOGPFAULTERRORBOX);
 
     get_version();
@@ -2464,10 +2452,8 @@ typedef struct	{
     char pipech;	/* one char buffer for handles opened on pipes */
     int lockinitflag;
     CRITICAL_SECTION lock;
-#if RUBY_MSVCRT_VERSION >= 80
     char textmode;
     char pipech2[2];
-#endif
 }	ioinfo;
 #endif
 
@@ -2492,7 +2478,6 @@ static inline ioinfo* _pioinfo(int);
 #define rb_acrt_lowio_lock_fh(i)   EnterCriticalSection(&_pioinfo(i)->lock)
 #define rb_acrt_lowio_unlock_fh(i) LeaveCriticalSection(&_pioinfo(i)->lock)
 
-#if RUBY_MSVCRT_VERSION >= 80
 static size_t pioinfo_extra = 0;	/* workaround for VC++8 SP1 */
 
 /* License: Ruby's */
@@ -2656,9 +2641,6 @@ set_pioinfo_extra(void)
         pioinfo_extra = 0;
     }
 }
-#else
-#define pioinfo_extra 0
-#endif
 
 static inline ioinfo*
 _pioinfo(int fd)
@@ -4235,7 +4217,6 @@ socketpair(int af, int type, int protocol, int *sv)
     return 0;
 }
 
-#if !defined(_MSC_VER) || _MSC_VER >= 1400
 /* License: Ruby's */
 static void
 str2guid(const char *str, GUID *guid)
@@ -4361,7 +4342,6 @@ freeifaddrs(struct ifaddrs *ifp)
         ifp = next;
     }
 }
-#endif
 
 #if 0 // Have never been used
 //
@@ -7592,20 +7572,6 @@ rb_w32_write_console(uintptr_t strarg, int fd)
     return (long)reslen;
 }
 
-#if RUBY_MSVCRT_VERSION < 80 && !defined(HAVE__GMTIME64_S)
-/* License: Ruby's */
-static int
-unixtime_to_filetime(time_t time, FILETIME *ft)
-{
-    ULARGE_INTEGER tmp;
-
-    tmp.QuadPart = unix_to_filetime((ULONGLONG)time);
-    ft->dwLowDateTime = tmp.LowPart;
-    ft->dwHighDateTime = tmp.HighPart;
-    return 0;
-}
-#endif
-
 /* License: Ruby's */
 static int
 timespec_to_filetime(const struct timespec *ts, FILETIME *ft)
@@ -7982,23 +7948,6 @@ rb_w32_isatty(int fd)
     return 1;
 }
 
-#if defined(_MSC_VER) && RUBY_MSVCRT_VERSION <= 60
-extern long _ftol(double);
-/* License: Ruby's */
-long
-_ftol2(double d)
-{
-    return _ftol(d);
-}
-
-/* License: Ruby's */
-long
-_ftol2_sse(double d)
-{
-    return _ftol(d);
-}
-#endif
-
 #ifndef signbit
 /* License: Ruby's */
 int
@@ -8030,68 +7979,6 @@ rb_w32_fd_is_text(int fd)
     return _osfile(fd) & FTEXT;
 }
 
-#if RUBY_MSVCRT_VERSION < 80 && !defined(HAVE__GMTIME64_S)
-/* License: Ruby's */
-static int
-unixtime_to_systemtime(const time_t t, SYSTEMTIME *st)
-{
-    FILETIME ft;
-    if (unixtime_to_filetime(t, &ft)) return -1;
-    if (!FileTimeToSystemTime(&ft, st)) return -1;
-    return 0;
-}
-
-/* License: Ruby's */
-static void
-systemtime_to_tm(const SYSTEMTIME *st, struct tm *t)
-{
-    int y = st->wYear, m = st->wMonth, d = st->wDay;
-    t->tm_sec  = st->wSecond;
-    t->tm_min  = st->wMinute;
-    t->tm_hour = st->wHour;
-    t->tm_mday = st->wDay;
-    t->tm_mon  = st->wMonth - 1;
-    t->tm_year = y - 1900;
-    t->tm_wday = st->wDayOfWeek;
-    switch (m) {
-      case 1:
-        break;
-      case 2:
-        d += 31;
-        break;
-      default:
-        d += 31 + 28 + (!(y % 4) && ((y % 100) || !(y % 400)));
-        d += ((m - 3) * 153 + 2) / 5;
-        break;
-    }
-    t->tm_yday = d - 1;
-}
-
-/* License: Ruby's */
-static int
-systemtime_to_localtime(TIME_ZONE_INFORMATION *tz, SYSTEMTIME *gst, SYSTEMTIME *lst)
-{
-    TIME_ZONE_INFORMATION stdtz;
-    SYSTEMTIME sst;
-
-    if (!SystemTimeToTzSpecificLocalTime(tz, gst, lst)) return -1;
-    if (!tz) {
-        GetTimeZoneInformation(&stdtz);
-        tz = &stdtz;
-    }
-    if (tz->StandardBias == tz->DaylightBias) return 0;
-    if (!tz->StandardDate.wMonth) return 0;
-    if (!tz->DaylightDate.wMonth) return 0;
-    if (tz != &stdtz) stdtz = *tz;
-
-    stdtz.StandardDate.wMonth = stdtz.DaylightDate.wMonth = 0;
-    if (!SystemTimeToTzSpecificLocalTime(&stdtz, gst, &sst)) return 0;
-    if (lst->wMinute == sst.wMinute && lst->wHour == sst.wHour)
-        return 0;
-    return 1;
-}
-#endif
-
 #ifdef HAVE__GMTIME64_S
 # ifndef HAVE__LOCALTIME64_S
 /* assume same as _gmtime64_s() */
@@ -8115,17 +8002,8 @@ gmtime_r(const time_t *tp, struct tm *rp)
         errno = e;
         return NULL;
     }
-#if RUBY_MSVCRT_VERSION >= 80 || defined(HAVE__GMTIME64_S)
     e = gmtime_s(rp, tp);
     if (e != 0) goto error;
-#else
-    {
-        SYSTEMTIME st;
-        if (unixtime_to_systemtime(*tp, &st)) goto error;
-        rp->tm_isdst = 0;
-        systemtime_to_tm(&st, rp);
-    }
-#endif
     return rp;
 }
 
@@ -8139,17 +8017,8 @@ localtime_r(const time_t *tp, struct tm *rp)
         errno = e;
         return NULL;
     }
-#if RUBY_MSVCRT_VERSION >= 80 || defined(HAVE__LOCALTIME64_S)
     e = localtime_s(rp, tp);
     if (e) goto error;
-#else
-    {
-        SYSTEMTIME gst, lst;
-        if (unixtime_to_systemtime(*tp, &gst)) goto error;
-        rp->tm_isdst = systemtime_to_localtime(NULL, &gst, &lst);
-        systemtime_to_tm(&lst, rp);
-    }
-#endif
     return rp;
 }