diff --git a/embed.fnc b/embed.fnc
index 89533d2f35..ba86b15fe7 100644
--- a/embed.fnc
+++ b/embed.fnc
@@ -4537,11 +4537,12 @@ op	|void	|sv_add_backref |NN SV * const tsv			\
 				|NN SV * const sv
 #endif
 #if defined(PERL_IN_GV_C) || defined(PERL_IN_UNIVERSAL_C)
-EGdp	|HV *	|gv_stashsvpvn_cached					\
-				|SV *namesv				\
-				|const char *name			\
+Edp	|HV *	|gv_stashsvpvn_cached					\
+				|NULLOK SV *namesv			\
+				|NULLOK const char *name		\
 				|U32 namelen				\
-				|I32 flags
+				|I32 flags				\
+				assert(namesv || name)
 #endif
 #if defined(PERL_IN_HV_C)
 Sx	|void	|clear_placeholders					\
@@ -6120,17 +6121,19 @@ S	|I32	|utf16_textfilter					\
 # endif
 #endif /* defined(PERL_IN_TOKE_C) */
 #if defined(PERL_IN_UNIVERSAL_C)
-GS	|bool	|isa_lookup	|NULLOK NOCHECK HV *stash		\
+S	|bool	|isa_lookup	|NN HV *stash				\
 				|NULLOK SV *namesv			\
 				|NULLOK const char *name		\
 				|STRLEN len				\
-				|U32 flags
-GS	|bool	|sv_derived_from_svpvn					\
-				|NULLOK SV *sv				\
+				|U32 flags				\
+				assert(namesv || name)
+S	|bool	|sv_derived_from_svpvn					\
+				|NN SV *sv				\
 				|NULLOK SV *namesv			\
 				|NULLOK const char *name		\
 				|const STRLEN len			\
-				|U32 flags
+				|U32 flags				\
+				assert(namesv || name)
 #endif
 #if defined(PERL_IN_UTF8_C)
 RS	|UV	|check_locale_boundary_crossing 			\
diff --git a/gv.c b/gv.c
index a5960c82f8..e494bc3096 100644
--- a/gv.c
+++ b/gv.c
@@ -1691,17 +1691,14 @@ reasons.
 =cut
 */
 
-#define PERL_ARGS_ASSERT_GV_STASHSVPVN_CACHED \
-    assert(namesv || name)
-
 HV*
 Perl_gv_stashsvpvn_cached(pTHX_ SV *namesv, const char *name, U32 namelen, I32 flags)
 {
+    PERL_ARGS_ASSERT_GV_STASHSVPVN_CACHED;
+
     HV* stash;
     HE* he;
 
-    PERL_ARGS_ASSERT_GV_STASHSVPVN_CACHED;
-
     he = (HE *)hv_common(
         PL_stashcache, namesv, name, namelen,
         (flags & SVf_UTF8) ? HVhek_UTF8 : 0, 0, NULL, 0
diff --git a/proto.h b/proto.h
index ca17ecfe74..41eabb9a75 100644
--- a/proto.h
+++ b/proto.h
@@ -6950,6 +6950,8 @@ Perl_sv_add_backref(pTHX_ SV * const tsv, SV * const sv)
 PERL_CALLCONV HV *
 Perl_gv_stashsvpvn_cached(pTHX_ SV *namesv, const char *name, U32 namelen, I32 flags)
         __attribute__visibility__("hidden");
+# define PERL_ARGS_ASSERT_GV_STASHSVPVN_CACHED  \
+        assert(namesv || name)
 
 #endif
 #if defined(PERL_IN_HV_C)
@@ -9470,11 +9472,15 @@ S_utf16_textfilter(pTHX_ int idx, SV *sv, int maxlen);
 #if defined(PERL_IN_UNIVERSAL_C)
 STATIC bool
 S_isa_lookup(pTHX_ HV *stash, SV *namesv, const char *name, STRLEN len, U32 flags);
+# define PERL_ARGS_ASSERT_ISA_LOOKUP            \
+        assert(stash); assert(SvTYPE(stash) == SVt_PVHV); assert(namesv || name)
 
 STATIC bool
 S_sv_derived_from_svpvn(pTHX_ SV *sv, SV *namesv, const char *name, const STRLEN len, U32 flags);
+# define PERL_ARGS_ASSERT_SV_DERIVED_FROM_SVPVN \
+        assert(sv); assert(namesv || name)
 
-#endif
+#endif /* defined(PERL_IN_UNIVERSAL_C) */
 #if defined(PERL_IN_UTF8_C)
 STATIC UV
 S__to_utf8_case(pTHX_ const UV original, const U8 *p, U8 *ustrp, STRLEN *lenp, SV *invlist, const I32 * const invmap, const U32 * const * const aux_tables, const U8 * const aux_table_lengths, const char * const normal);
diff --git a/universal.c b/universal.c
index d60bf9585e..34e5e66690 100644
--- a/universal.c
+++ b/universal.c
@@ -39,20 +39,15 @@
  * The main guts of traverse_isa was actually copied from gv_fetchmeth
  */
 
-#define PERL_ARGS_ASSERT_ISA_LOOKUP \
-    assert(stash); \
-    assert(namesv || name)
-
-
 STATIC bool
 S_isa_lookup(pTHX_ HV *stash, SV *namesv, const char * name, STRLEN len, U32 flags)
 {
+    PERL_ARGS_ASSERT_ISA_LOOKUP;
+
     const struct mro_meta *const meta = HvMROMETA(stash);
     HV *isa = meta->isa;
     const HV *our_stash;
 
-    PERL_ARGS_ASSERT_ISA_LOOKUP;
-
     if (!isa) {
         (void)mro_get_linear_isa(stash);
         isa = meta->isa;
@@ -83,10 +78,6 @@ S_isa_lookup(pTHX_ HV *stash, SV *namesv, const char * name, STRLEN len, U32 fla
     return FALSE;
 }
 
-#define PERL_ARGS_ASSERT_SV_DERIVED_FROM_SVPVN \
-    assert(sv); \
-    assert(namesv || name)
-
 STATIC bool
 S_sv_derived_from_svpvn(pTHX_ SV *sv, SV *namesv, const char * name, const STRLEN len, U32 flags)
 {