--- a/memory/build/zone.c
+++ b/memory/build/zone.c
@@ -248,40 +248,40 @@ zone_force_lock(malloc_zone_t *zone)
   if (isthreaded)
     jemalloc_prefork();
 }
 
 static void
 zone_force_unlock(malloc_zone_t *zone)
 {
   /* /!\ This calls into jemalloc. It works because we're linked in the
-   * same library. Stolen from jemalloc's zone.c. */
+   * same library. Stolen from jemalloc's zone.c. See the comment there. */
   if (isthreaded)
-    jemalloc_postfork_parent();
+    jemalloc_postfork_child();
 }
 
 #else
 
 extern void _malloc_prefork(void);
-extern void _malloc_postfork(void);
+extern void _malloc_postfork_child(void);
 
 static void
 zone_force_lock(malloc_zone_t *zone)
 {
   /* /!\ This calls into mozjemalloc. It works because we're linked in the
    * same library. */
   _malloc_prefork();
 }
 
 static void
 zone_force_unlock(malloc_zone_t *zone)
 {
   /* /!\ This calls into mozjemalloc. It works because we're linked in the
    * same library. */
-  _malloc_postfork();
+  _malloc_postfork_child();
 }
 
 #endif
 
 static void
 zone_statistics(malloc_zone_t *zone, malloc_statistics_t *stats)
 {
   /* We make no effort to actually fill the values */

--- a/memory/mozjemalloc/jemalloc.c
+++ b/memory/mozjemalloc/jemalloc.c
@@ -1453,17 +1453,21 @@ bool		malloc_init_hard(void);
 
 #ifndef MOZ_MEMORY_DARWIN
 static
 #endif
 void	_malloc_prefork(void);
 #ifndef MOZ_MEMORY_DARWIN
 static
 #endif
-void	_malloc_postfork(void);
+void	_malloc_postfork_parent(void);
+#ifndef MOZ_MEMORY_DARWIN
+static
+#endif
+void	_malloc_postfork_child(void);
 
 /*
  * End function prototypes.
  */
 /******************************************************************************/
 
 static inline size_t
 load_acquire_z(size_t *p)
@@ -6034,17 +6038,17 @@ MALLOC_OUT:
 	if (chunk_rtree == NULL)
 		return (true);
 #endif
 
 	malloc_initialized = true;
 
 #if !defined(MOZ_MEMORY_WINDOWS) && !defined(MOZ_MEMORY_DARWIN)
 	/* Prevent potential deadlock on malloc locks after fork. */
-	pthread_atfork(_malloc_prefork, _malloc_postfork, _malloc_postfork);
+	pthread_atfork(_malloc_prefork, _malloc_postfork_parent, _malloc_postfork_child);
 #endif
 
 #if defined(NEEDS_PTHREAD_MMAP_UNALIGNED_TSD)
 	if (pthread_key_create(&mmap_unaligned_tsd, NULL) != 0) {
 		malloc_printf("<jemalloc>: Error in pthread_key_create()\n");
 	}
 #endif
 
@@ -6779,33 +6783,54 @@ void
 
 	malloc_mutex_lock(&huge_mtx);
 }
 
 #ifndef MOZ_MEMORY_DARWIN
 static
 #endif
 void
-_malloc_postfork(void)
+_malloc_postfork_parent(void)
 {
 	unsigned i;
 
 	/* Release all mutexes, now that fork() has completed. */
 
 	malloc_mutex_unlock(&huge_mtx);
 
 	malloc_mutex_unlock(&base_mtx);
 
 	for (i = 0; i < narenas; i++) {
 		if (arenas[i] != NULL)
 			malloc_spin_unlock(&arenas[i]->lock);
 	}
 	malloc_spin_unlock(&arenas_lock);
 }
 
+#ifndef MOZ_MEMORY_DARWIN
+static
+#endif
+void
+_malloc_postfork_child(void)
+{
+	unsigned i;
+
+	/* Reinitialize all mutexes, now that fork() has completed. */
+
+	malloc_mutex_init(&huge_mtx);
+
+	malloc_mutex_init(&base_mtx);
+
+	for (i = 0; i < narenas; i++) {
+		if (arenas[i] != NULL)
+			malloc_spin_init(&arenas[i]->lock);
+	}
+	malloc_spin_init(&arenas_lock);
+}
+
 /*
  * End library-private functions.
  */
 /******************************************************************************/
 
 #ifdef HAVE_DLOPEN
 #  include <dlfcn.h>
 #endif