diff --git a/pp.h b/pp.h
index 76d29202b2..21ed3b8fbb 100644
--- a/pp.h
+++ b/pp.h
@@ -397,27 +397,27 @@ Does not use C<TARG>.  See also C<L</XPUSHu>>, C<L</mPUSHu>> and C<L</PUSHu>>.
 #  define EXTEND_HWM_SET(p, n) NOOP
 #endif
 
-/* _EXTEND_SAFE_N(n): private helper macro for EXTEND().
+/* EXTEND_SAFE_N_(n): private helper macro for EXTEND().
  * Tests whether the value of n would be truncated when implicitly cast to
  * SSize_t as an arg to stack_grow(). If so, sets it to -1 instead to
  * trigger a panic. It will be constant folded on platforms where this
  * can't happen.
  */
 
-#define _EXTEND_SAFE_N(n) \
+#define EXTEND_SAFE_N_(n) \
         (sizeof(n) > sizeof(SSize_t) && ((SSize_t)(n) != (n)) ? -1 : (n))
 
 #ifdef STRESS_REALLOC
 # define EXTEND_SKIP(p, n) EXTEND_HWM_SET(p, n)
 
 # define EXTEND(p,n)   STMT_START {                                     \
-                           sp = stack_grow(sp,p,_EXTEND_SAFE_N(n));     \
+                           sp = stack_grow(sp,p,EXTEND_SAFE_N_(n));     \
                            PERL_UNUSED_VAR(sp);                         \
                        } STMT_END
 /* Same thing, but update mark register too. */
 # define MEXTEND(p,n)   STMT_START {                                    \
                             const SSize_t markoff = mark - PL_stack_base; \
-                            sp = stack_grow(sp,p,_EXTEND_SAFE_N(n));    \
+                            sp = stack_grow(sp,p,EXTEND_SAFE_N_(n));    \
                             mark = PL_stack_base + markoff;             \
                             PERL_UNUSED_VAR(sp);                        \
                         } STMT_END
@@ -459,7 +459,7 @@ Does not use C<TARG>.  See also C<L</XPUSHu>>, C<L</mPUSHu>> and C<L</PUSHu>>.
 #  define EXTEND(p,n)   STMT_START {                                    \
                          EXTEND_HWM_SET(p, n);                          \
                          if (UNLIKELY(_EXTEND_NEEDS_GROW(p,n))) {       \
-                           sp = stack_grow(sp,p,_EXTEND_SAFE_N(n));     \
+                           sp = stack_grow(sp,p,EXTEND_SAFE_N_(n));     \
                            PERL_UNUSED_VAR(sp);                         \
                          }                                              \
                         } STMT_END
@@ -468,7 +468,7 @@ Does not use C<TARG>.  See also C<L</XPUSHu>>, C<L</mPUSHu>> and C<L</PUSHu>>.
                          EXTEND_HWM_SET(p, n);                          \
                          if (UNLIKELY(_EXTEND_NEEDS_GROW(p,n))) {       \
                            const SSize_t markoff = mark - PL_stack_base;\
-                           sp = stack_grow(sp,p,_EXTEND_SAFE_N(n));     \
+                           sp = stack_grow(sp,p,EXTEND_SAFE_N_(n));     \
                            mark = PL_stack_base + markoff;              \
                            PERL_UNUSED_VAR(sp);                         \
                          }                                              \