diff --git a/js/src/jsgc.cpp b/js/src/jsgc.cpp
index 6adedacad56..15ebffebd4c 100644
--- a/js/src/jsgc.cpp
+++ b/js/src/jsgc.cpp
@@ -911,6 +911,11 @@ struct JSGCLockHashEntry : public JSDHashEntryHdr
 JSBool
 js_InitGC(JSRuntime *rt, uint32 maxbytes)
 {
+#if defined(XP_WIN) && defined(_M_X64)
+    if (!InitNtAllocAPIs())
+        return JS_FALSE;
+#endif
+    
     InitGCArenaLists(rt);
     if (!rt->gcRootsHash.init(GC_ROOTS_SIZE))
         return false;
diff --git a/js/src/jsgcchunk.cpp b/js/src/jsgcchunk.cpp
index a833dcb84b2..d69fe03c50c 100644
--- a/js/src/jsgcchunk.cpp
+++ b/js/src/jsgcchunk.cpp
@@ -140,6 +140,47 @@ UnmapPages(void *p, size_t size)
 
 # else /* WINCE */
 
+#  ifdef _M_X64
+
+typedef long (*ntavm_fun)(HANDLE handle, void **addr, ULONG zbits,
+                          size_t *size, ULONG alloctype, ULONG prot);
+typedef long (*ntfvm_fun)(HANDLE handle, void **addr, size_t *size, 
+                          ULONG freetype);
+
+static ntavm_fun NtAllocateVirtualMemory;
+static ntfvm_fun NtFreeVirtualMemory;
+
+bool 
+js::InitNtAllocAPIs()
+{
+    HMODULE h = GetModuleHandle("ntdll.dll");
+    if (!h)
+        return false;
+    NtAllocateVirtualMemory = ntavm_fun(GetProcAddress(h, "NtAllocateVirtualMemory"));
+    if (!NtAllocateVirtualMemory)
+        return false;
+    NtFreeVirtualMemory = ntfvm_fun(GetProcAddress(h, "NtFreeVirtualMemory"));
+    if (!NtFreeVirtualMemory)
+        return false;
+}
+
+// Allocate pages with 32-bit addresses (i.e., top 16 bits are all 0).
+static void *
+MapPages(void *addr, size_t size)
+{
+    long rc = NtAllocateVirtualMemory(INVALID_HANDLE_VALUE, &addr, 1, &size,
+                                      MEM_COMMIT|MEM_RESERVE, PAGE_READWRITE);
+    return rc ? NULL : addr;
+}
+
+static void
+UnmapPages(void *addr, size_t size)
+{
+    NtFreeVirtualMemory(INVALID_HANDLE_VALUE, &addr, &size, MEM_RELEASE);
+}
+
+#  else /* _M_X64 */
+
 static void *
 MapPages(void *addr, size_t size)
 {
@@ -154,6 +195,8 @@ UnmapPages(void *addr, size_t size)
     JS_ALWAYS_TRUE(VirtualFree(addr, 0, MEM_RELEASE));
 }
 
+#  endif /* _M_X64 */
+
 # endif /* !WINCE */
 
 #elif defined(XP_MACOSX) || defined(DARWIN)
diff --git a/js/src/jsgcchunk.h b/js/src/jsgcchunk.h
index bb8622d9b68..3c2d38dc983 100644
--- a/js/src/jsgcchunk.h
+++ b/js/src/jsgcchunk.h
@@ -55,6 +55,10 @@ const size_t GC_CHUNK_SHIFT = 20;
 const size_t GC_CHUNK_SIZE = size_t(1) << GC_CHUNK_SHIFT;
 const size_t GC_CHUNK_MASK = GC_CHUNK_SIZE - 1;
 
+#if defined(XP_WIN) && defined(_M_X64)
+bool InitNtAllocAPIs();
+#endif
+
 void *
 AllocGCChunk();