diff --git a/configure.ac b/configure.ac
index 57072d2..5fbe9cc 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1,11 +1,11 @@
 dnl Process this file with autoconf to produce a configure script.
 AC_INIT(diff.h)
-AC_CONFIG_HEADER(config.h)
+AC_CONFIG_HEADER(config.h:config.hin)
 AC_PROG_CC
 AC_PROG_CPP
 AC_PROG_INSTALL
-AC_OS_ISC
-AC_OS_MINIX
+AC_ISC_POSIX
+AC_MINIX
 AC_C_CONST
 AC_HEADER_STDC
 AC_CHECK_HEADERS(unistd.h fcntl.h limits.h stdlib.h string.h sys/file.h sys/wait.h time.h)
@@ -13,10 +13,11 @@ AC_HEADER_DIRENT
 AC_HEADER_STAT
 AC_TYPE_PID_T
 AC_TYPE_SIGNAL
-AC_CHECK_FUNCS(dup2 sigaction strerror memchr)
+AC_CHECK_FUNCS(dup2 memchr sigaction strchr strerror)
 AC_REPLACE_FUNCS(memchr waitpid)
 AC_FUNC_ALLOCA
 AC_FUNC_CLOSEDIR_VOID
+dnl No need for AC_FUNC_MEMCMP, since memcmp is used only to test for equality.
 AC_FUNC_VFORK
 AC_FUNC_VPRINTF
 AC_STRUCT_ST_BLKSIZE