diff --git a/perl.h b/perl.h
index 7becbb382b50..53942a1ee85d 100644
--- a/perl.h
+++ b/perl.h
@@ -6767,7 +6767,31 @@ the plain locale pragma without a parameter (S<C<use locale>>) is in effect.
 #  define PORCELAIN_SETLOCALE_UNLOCK    gwLOCALE_UNLOCK
 #endif
 
-/* This was defined above for the case where locales aren't thread safe. */
+/* Similar to gwLOCALE_LOCK, there are functions that require both the locale
+ * and environment to be constant during their execution, and don't change
+ * either of those things, but do write to some sort of shared global space.
+ * They require some sort of exclusive lock against similar functions, and a
+ * read lock on both the locale and environment.  However, on systems which
+ * have per-thread locales, the locale is constant during the execution of
+ * these functions, and so no locale lock is necssary.  For such systems, an
+ * exclusive ENV lock is necessary and sufficient.  On systems where the locale
+ * could change out from under us, we use an exclusive LOCALE lock to prevent
+ * that, and a read ENV lock to prevent other threads that have nothing to do
+ * with locales here from changing the environment. */
+#ifdef SETLOCALE_LOCK
+#  define gwENVr_LOCALEr_LOCK                                               \
+                    STMT_START { SETLOCALE_LOCK; ENV_READ_LOCK; } STMT_END
+#  define gwENVr_LOCALEr_UNLOCK                                             \
+                STMT_START { ENV_READ_UNLOCK; SETLOCALE_UNLOCK; } STMT_END
+#else
+#  define gwENVr_LOCALEr_LOCK           ENV_LOCK
+#  define gwENVr_LOCALEr_UNLOCK         ENV_UNLOCK
+#endif
+
+/* Now that we have defined gwENVr_LOCALEr_LOCK, we can finish defining
+ * SETLOCALE_LOCK, which we kept undefined until here on a thread-safe system
+ * so that we could use that fact to calculate what gwENVr_LOCALEr_LOCK should
+ * be */
 #ifndef SETLOCALE_LOCK
 #  define SETLOCALE_LOCK                NOOP
 #  define SETLOCALE_UNLOCK              NOOP
@@ -6777,12 +6801,38 @@ the plain locale pragma without a parameter (S<C<use locale>>) is in effect.
 #define LOCALE_READ_LOCK                SETLOCALE_LOCK
 #define LOCALE_READ_UNLOCK              SETLOCALE_UNLOCK
 
-
 #ifndef LC_NUMERIC_LOCK
 #  define LC_NUMERIC_LOCK(cond)   NOOP
 #  define LC_NUMERIC_UNLOCK       NOOP
 #endif
 
+#ifdef LC_CTYPE_LOCK
+#  ifdef HAS_MBLEN
+#    define MBLEN_LOCK_                 LC_CTYPE_LOCK
+#    define MBLEN_UNLOCK_               LC_CTYPE_UNLOCK
+#  endif
+#  ifdef HAS_MBRLEN
+#    define MBRLEN_LOCK_                LC_CTYPE_LOCK
+#    define MBRLEN_UNLOCK_              LC_CTYPE_UNLOCK
+#  endif
+#  ifdef HAS_MBTOWC
+#    define MBTOWC_LOCK_                LC_CTYPE_LOCK
+#    define MBTOWC_UNLOCK_              LC_CTYPE_UNLOCK
+#  endif
+#  ifdef HAS_MBRTOWC
+#    define MBRTOWC_LOCK_               LC_CTYPE_LOCK
+#    define MBRTOWC_UNLOCK_             LC_CTYPE_UNLOCK
+#  endif
+#  ifdef HAS_WCTOMB
+#    define WCTOMB_LOCK_                LC_CTYPE_LOCK
+#    define WCTOMB_UNLOCK_              LC_CTYPE_UNLOCK
+#  endif
+#  ifdef HAS_WCRTOMB
+#    define WCRTOMB_LOCK_               LC_CTYPE_LOCK
+#    define WCRTOMB_UNLOCK_             LC_CTYPE_UNLOCK
+#  endif
+#endif
+
 #  define MBLEN_LOCK_                gwLOCALE_LOCK
 #  define MBLEN_UNLOCK_              gwLOCALE_UNLOCK