diff --git a/memory/jemalloc/jemalloc.c b/memory/jemalloc/jemalloc.c
--- a/memory/jemalloc/jemalloc.c
+++ b/memory/jemalloc/jemalloc.c
@@ -1830,19 +1830,16 @@ base_pages_alloc_mmap(size_t minsize)
 	if (opt_pagefile) {
 		pfd = pagefile_init(csize);
 		if (pfd == -1)
 			return (true);
 	} else
 #endif
 		pfd = -1;
 	base_pages = pages_map(NULL, csize, pfd);
-#ifdef MOZ_MEMORY_WINCE
-	pages_commit(base_pages, csize);
-#endif
 	if (base_pages == NULL) {
 		ret = true;
 		goto RETURN;
 	}
 	base_next_addr = base_pages;
 	base_past_addr = (void *)((uintptr_t)base_pages + csize);
 #ifdef MALLOC_DECOMMIT
 	/*
@@ -2162,37 +2159,64 @@ rb_wrap(static, extent_tree_ad_, extent_
  */
 
 #ifdef MOZ_MEMORY_WINDOWS
 static void *
 pages_map(void *addr, size_t size, int pfd)
 {
 	void *ret;
 #if defined(MOZ_MEMORY_WINCE)
+	size_t offset;
+
+	if (addr)
+		DebugBreak(); /* XXX assert */
+
 	ret = VirtualAlloc(addr, size, MEM_RESERVE, PAGE_NOACCESS);
+
+	offset = CHUNK_ADDR2OFFSET(ret);
+	if (offset == 0) {
+		VirtualAlloc(ret, size, MEM_COMMIT, PAGE_READWRITE);
+	} else {
+		VirtualFree(addr, 0, MEM_RELEASE);
+
+		/*
+		 * Over-allocate in order to map a memory region that
+		 * is definitely large enough.
+		 */
+		ret = VirtualAlloc(NULL, size + chunksize, PAGE_NOACCESS);
+		if (ret == NULL)
+			return NULL;
+
+		/* XXX we need to store the actual 'ret' somewhere */
+		offset = CHUNK_ADDR2OFFSET(ret);
+		ret = ret + offset; /* XXX should this be -? */
+		VirtualAlloc(ret, size - offset, MEM_COMMIT, PAGE_READWRITE);
+	}
 #elif defined(MOZ_MEMORY_WINDOWS)
 	ret = VirtualAlloc(addr, size, MEM_COMMIT | MEM_RESERVE,
 	    PAGE_READWRITE);
 #endif
 	return (ret);
 }
 
 static void
 pages_unmap(void *addr, size_t size)
 {
 #ifdef MOZ_MEMORY_WINCE
-	VirtualFree(addr, size, MEM_RELEASE);
-#else
+	MEMORY_BASIC_INFORMATION info;
+	VirtualQuery(addr, &info, sizeof(info));
+	addr = info.BaseAddress;
+#endif
 	if (VirtualFree(addr, 0, MEM_RELEASE) == 0) {
 		_malloc_message(_getprogname(),
 		    ": (malloc) Error in VirtualFree()\n", "", "");
 		if (opt_abort)
 			abort();
 	}
-#endif
+
 }
 #elif (defined(MOZ_MEMORY_DARWIN))
 static void *
 pages_map(void *addr, size_t size, int pfd)
 {
 	void *ret;
 	kern_return_t err;
 	int flags;
@@ -2498,19 +2522,16 @@ chunk_alloc_mmap(size_t size, bool pagef
 				    chunksize - offset), size, pfd);
 			}
 			/*
 			 * Failure here indicates a race with another thread, so
 			 * try again.
 			 */
 		}
 	}
-#ifdef MOZ_MEMORY_WINCE
-	pages_commit(ret, size);
-#endif
 RETURN:
 #endif
 #ifdef MALLOC_PAGEFILE
 	if (pfd != -1)
 		pagefile_close(pfd);
 #endif
 #ifdef MALLOC_STATS
 	if (ret != NULL)
@@ -5011,19 +5032,16 @@ huge_palloc(size_t alignment, size_t siz
 		ret = (void *)((uintptr_t)over + offset);
 		chunk_dealloc(over, alloc_size);
 		ret = pages_map(ret, chunk_size, pfd);
 		/*
 		 * Failure here indicates a race with another thread, so try
 		 * again.
 		 */
 	} while (ret == NULL);
-#ifdef MOZ_MEMORY_WINCE
-	pages_commit(ret, chunk_size);
-#endif
 	/* Insert node into huge. */
 	node->addr = ret;
 #ifdef MALLOC_DECOMMIT
 	psize = PAGE_CEILING(size);
 	node->size = psize;
 #else
 	node->size = chunk_size;
 #endif