diff --git a/tools/trace-malloc/lib/nsDebugHelpWin32.cpp b/tools/trace-malloc/lib/nsDebugHelpWin32.cpp
index 10b3951218f..afc7f415f1e 100644
--- a/tools/trace-malloc/lib/nsDebugHelpWin32.cpp
+++ b/tools/trace-malloc/lib/nsDebugHelpWin32.cpp
@@ -37,7 +37,7 @@
  * ***** END LICENSE BLOCK ***** */
 
 
-#if defined(_WIN32) && defined(_M_IX86)
+#if defined(_WIN32) && (defined(_M_IX86) || defined(_M_X64))
 // This is the .cpp file where the globals live
 #define DHW_IMPLEMENT_GLOBALS
 #include <stdio.h>
@@ -49,7 +49,7 @@
 #include "nscore.h"
 #include "nsDebugHelpWin32.h"
 #else
-#error "nsDebugHelpWin32.cpp should only be built in Win32 x86 builds"
+#error "nsDebugHelpWin32.cpp should only be built in Win32 x86/x64 builds"
 #endif
 
 
@@ -84,7 +84,11 @@ dhwEnsureImageHlpInitialized()
     dhw##name_ = (typename_) ::GetProcAddress(module, #name_); \
     if(!dhw##name_) return PR_FALSE;
 
+#ifdef _WIN64
+    INIT_PROC(ENUMERATELOADEDMODULES64, EnumerateLoadedModules64);
+#else
     INIT_PROC(ENUMERATELOADEDMODULES, EnumerateLoadedModules);
+#endif
     INIT_PROC(IMAGEDIRECTORYENTRYTODATA, ImageDirectoryEntryToData);
 
 #undef INIT_PROC
@@ -208,10 +212,17 @@ DHWImportHooker::~DHWImportHooker()
         PR_Unlock(gLock);
 }    
 
+#ifdef _WIN64
+static BOOL CALLBACK ModuleEnumCallback(PCSTR ModuleName,
+                                        DWORD64 ModuleBase,
+                                        ULONG ModuleSize,
+                                        PVOID UserContext)
+#else
 static BOOL CALLBACK ModuleEnumCallback(PCSTR ModuleName,
                                         ULONG ModuleBase,
                                         ULONG ModuleSize,
                                         PVOID UserContext)
+#endif
 {
     //printf("Module Name %s\n",ModuleName);
     DHWImportHooker* self = (DHWImportHooker*) UserContext;
@@ -226,8 +237,13 @@ DHWImportHooker::PatchAllModules()
     // constness of the first parameter of PENUMLOADED_MODULES_CALLBACK
     // varies over SDK versions (from non-const to const over time).
     // See bug 391848 and bug 415426.
+#ifdef _WIN64
+    return dhwEnumerateLoadedModules64(::GetCurrentProcess(),
+               (PENUMLOADED_MODULES_CALLBACK64)ModuleEnumCallback, this);
+#else
     return dhwEnumerateLoadedModules(::GetCurrentProcess(), 
                (PENUMLOADED_MODULES_CALLBACK)ModuleEnumCallback, this);
+#endif
 }    
                                 
 PRBool 
diff --git a/tools/trace-malloc/lib/nsDebugHelpWin32.h b/tools/trace-malloc/lib/nsDebugHelpWin32.h
index d8dc2989614..585addb37c8 100644
--- a/tools/trace-malloc/lib/nsDebugHelpWin32.h
+++ b/tools/trace-malloc/lib/nsDebugHelpWin32.h
@@ -36,12 +36,12 @@
  *
  * ***** END LICENSE BLOCK ***** */
 
-/* Win32 x86 code for stack walking, symbol resolution, and function hooking */
+/* Win32 x86/x64 code for stack walking, symbol resolution, and function hooking */
 
 #ifndef __nsDebugHelpWin32_h__
 #define __nsDebugHelpWin32_h__
 
-#if defined(_WIN32) && defined(_M_IX86)
+#if defined(_WIN32) && (defined(_M_IX86) || defined(_M_X64))
   #ifndef WIN32_LEAN_AND_MEAN
     #define WIN32_LEAN_AND_MEAN
   #endif
@@ -49,7 +49,7 @@
   #include <imagehlp.h>
   #include <crtdbg.h>
 #else
-  #error "nsDebugHelpWin32.h should only be included in Win32 x86 builds"
+  #error "nsDebugHelpWin32.h should only be included in Win32 x86/x64 builds"
 #endif
 
 // XXX temporary hack...
@@ -122,8 +122,13 @@ DHW_DECLARE_FUN_TYPE_AND_GLOBAL(SYMGETSYMFROMADDRPROC, SymGetSymFromAddr, \
 
 #endif
 
+#ifndef _WIN64
 DHW_DECLARE_FUN_TYPE_AND_GLOBAL(ENUMERATELOADEDMODULES, EnumerateLoadedModules, \
                                 BOOL, __stdcall, (HANDLE, PENUMLOADED_MODULES_CALLBACK, PVOID));
+#else
+DHW_DECLARE_FUN_TYPE_AND_GLOBAL(ENUMERATELOADEDMODULES64, EnumerateLoadedModules64, \
+                                BOOL, __stdcall, (HANDLE, PENUMLOADED_MODULES_CALLBACK64, PVOID));
+#endif
 
 DHW_DECLARE_FUN_TYPE_AND_GLOBAL(IMAGEDIRECTORYENTRYTODATA, ImageDirectoryEntryToData, \
                                 PVOID, __stdcall, (PVOID, BOOL, USHORT, PULONG));