--- a/memory/build/mozmemory_wrap.c
+++ b/memory/build/mozmemory_wrap.c
@@ -63,16 +63,17 @@ mozmem_malloc_impl(_ZdaPvRKSt9nothrow_t)
 }
 #endif
 
 /* strndup and strdup may be defined as macros in string.h, which would
  * clash with the definitions below. */
 #undef strndup
 #undef strdup
 
+#ifndef XP_DARWIN
 MOZ_MEMORY_API char *
 strndup_impl(const char *src, size_t len)
 {
   char* dst = (char*) malloc_impl(len + 1);
   if (dst) {
     strncpy(dst, src, len);
     dst[len] = '\0';
   }
@@ -80,16 +81,17 @@ strndup_impl(const char *src, size_t len
 }
 
 MOZ_MEMORY_API char *
 strdup_impl(const char *src)
 {
   size_t len = strlen(src);
   return strndup_impl(src, len);
 }
+#endif /* XP_DARWIN */
 
 #ifdef ANDROID
 #include <stdarg.h>
 #include <stdio.h>
 
 MOZ_MEMORY_API int
 vasprintf_impl(char **str, const char *fmt, va_list ap)
 {

--- a/memory/build/mozmemory_wrap.h
+++ b/memory/build/mozmemory_wrap.h
@@ -48,20 +48,21 @@
  *   specific functions are left unprefixed. All these functions are however
  *   aliased when exporting them, such that the resulting mozglue.dll exports
  *   them unprefixed (see $(topsrcdir)/mozglue/build/mozglue.def.in). The
  *   prefixed malloc implementation and duplication functions are not
  *   exported.
  *
  * - On MacOSX, the system libc has a zone allocator, which allows us to
  *   hook custom malloc implementation functions without exporting them.
- *   However, since we want things in Firefox to skip the system zone
- *   allocator, the malloc implementation functions are all exported
- *   unprefixed, as well as duplication functions.
- *   Jemalloc-specific functions are also left unprefixed.
+ *   The malloc implementation functions are all prefixed with "je_" and used
+ *   this way from the custom zone allocator. They are not exported.
+ *   Duplication functions are not included, since they will call the custom
+ *   zone allocator anyways. Jemalloc-specific functions are also left
+ *   unprefixed.
  *
  * - On Android and Gonk, all functions are left unprefixed. Additionally,
  *   C++ allocation functions (operator new/delete) are also exported and
  *   unprefixed.
  *
  * - On other systems (mostly Linux), all functions are left unprefixed.
  *
  * Only Android and Gonk add C++ allocation functions.
@@ -128,17 +129,17 @@
 #endif
 
 #ifdef MOZ_MEMORY_IMPL
 #  if defined(MOZ_JEMALLOC_IMPL) && defined(MOZ_REPLACE_MALLOC)
 #    define mozmem_malloc_impl(a)     je_ ## a
 #    define mozmem_jemalloc_impl(a)   je_ ## a
 #  else
 #    define MOZ_JEMALLOC_API MOZ_EXTERN_C MFBT_API
-#    if defined(XP_WIN)
+#    if (defined(XP_WIN) || defined(XP_DARWIN))
 #      if defined(MOZ_REPLACE_MALLOC)
 #        define mozmem_malloc_impl(a)   a ## _impl
 #      else
 #        define mozmem_malloc_impl(a)   je_ ## a
 #      endif
 #    else
 #      define MOZ_MEMORY_API MOZ_EXTERN_C MFBT_API
 #      if defined(MOZ_WIDGET_ANDROID) || defined(MOZ_WIDGET_GONK)