diff --git a/embed.fnc b/embed.fnc
index 62a4957693df..87fafd4624d3 100644
--- a/embed.fnc
+++ b/embed.fnc
@@ -4411,7 +4411,7 @@ S	|HV *	|my_localeconv	|const int item
 S	|void	|populate_hash_from_localeconv				\
 				|NN HV *hv				\
 				|NN const char *locale			\
-				|const U32 which_mask			\
+				|const PERL_UINT_FAST8_T which_mask	\
 				|NN const lconv_offset_t *strings[2]	\
 				|NULLOK const lconv_offset_t *integers
 # endif
diff --git a/locale.c b/locale.c
index e03e727e360d..2656683cfe1a 100644
--- a/locale.c
+++ b/locale.c
@@ -5456,7 +5456,7 @@ S_my_localeconv(pTHX_ const int item)
     /* This is a mask, with one bit to tell S_populate_hash_from_localeconv to
      * populate the NUMERIC items; another bit for the MONETARY ones.  This way
      * it can choose which (or both) to populate from. */
-    U32 index_bits = 0;
+    PERL_UINT_FAST8_T index_bits = 0;
 
     /* This converts from a locale index to its bit position in the above mask.
      * */
@@ -5714,7 +5714,7 @@ S_populate_hash_from_localeconv(pTHX_ HV * hv,
 
                                       /* bit mask of which categories to
                                        * populate */
-                                      const U32 which_mask,
+                                      const PERL_UINT_FAST8_T which_mask,
 
                                       /* strings[0] points to the numeric
                                        * string fields; [1] to the monetary */
diff --git a/proto.h b/proto.h
index fb6e074dec0f..f71f72f91751 100644
--- a/proto.h
+++ b/proto.h
@@ -7023,7 +7023,7 @@ S_my_localeconv(pTHX_ const int item);
 #   define PERL_ARGS_ASSERT_MY_LOCALECONV
 
 STATIC void
-S_populate_hash_from_localeconv(pTHX_ HV *hv, const char *locale, const U32 which_mask, const lconv_offset_t *strings[2], const lconv_offset_t *integers);
+S_populate_hash_from_localeconv(pTHX_ HV *hv, const char *locale, const PERL_UINT_FAST8_T which_mask, const lconv_offset_t *strings[2], const lconv_offset_t *integers);
 #   define PERL_ARGS_ASSERT_POPULATE_HASH_FROM_LOCALECONV \
         assert(hv); assert(locale); assert(strings)