diff --git a/js/src/jsapi.cpp b/js/src/jsapi.cpp
index 6eb1b80d80c..b5c76978f5c 100644
--- a/js/src/jsapi.cpp
+++ b/js/src/jsapi.cpp
@@ -896,13 +896,12 @@ JS_SuspendRequest(JSContext *cx)
     if (saveDepth == 0)
         return 0;
 
+    JS_THREAD_DATA(cx)->conservativeGC.enable();
     do {
         cx->outstandingRequests++;  /* compensate for StopRequest */
         StopRequest(cx);
     } while (cx->requestDepth);
 
-    JS_THREAD_DATA(cx)->conservativeGC.enable();
-
     return saveDepth;
 #else
     return 0;
@@ -916,13 +915,12 @@ JS_ResumeRequest(JSContext *cx, jsrefcount saveDepth)
     if (saveDepth == 0)
         return;
 
-    JS_THREAD_DATA(cx)->conservativeGC.disable();
-
     JS_ASSERT(cx->outstandingRequests != 0);
     do {
         JS_BeginRequest(cx);
         cx->outstandingRequests--;  /* compensate for JS_BeginRequest */
     } while (--saveDepth != 0);
+    JS_THREAD_DATA(cx)->conservativeGC.disable();
 #endif
 }
 
diff --git a/js/src/jsgc.cpp b/js/src/jsgc.cpp
index 480c176d520..afa3da3937c 100644
--- a/js/src/jsgc.cpp
+++ b/js/src/jsgc.cpp
@@ -2462,6 +2462,7 @@ js_TraceRuntime(JSTracer *trc)
 #ifdef JS_THREADSAFE
             JS_ASSERT(acx->outstandingRequests != 0);
 #endif
+            JS_ASSERT(JS_THREAD_DATA(acx)->conservativeGC.isEnabled());
             void *thing;
             switch (gcr->tag) {
               default:
@@ -2496,8 +2497,16 @@ js_TraceRuntime(JSTracer *trc)
             if (!IsMarkedGCThing(thing)) {
                 ConservativeGCTest test = IsGCThingWord(rt, reinterpret_cast<jsuword>(thing));
                 fprintf(stderr,
-                        "Conservative GC scanner has missed the root %p with tag %ld"
-                        " on the stack due to %d. Aborting.\n", thing, (long) gcr->tag, int(test));
+                        "Conservative GC scanner has missed the root 0x%p with tag %ld"
+                        " on the stack due to %d. The root location 0x%p, distance from"
+                        " the stack base %ld, conservative gc span %ld."
+                        " Consevtaive GC status for the thread %d."
+                        " Aborting.\n",
+                        thing, (long) gcr->tag, int(test), (void *) gcr,
+                        (long) ((jsword) JS_THREAD_DATA(acx)->nativeStackBase - (jsword) gcr),
+                        (long) ((jsword) JS_THREAD_DATA(acx)->nativeStackBase -
+                                (jsword) JS_THREAD_DATA(acx)->conservativeGC.nativeStackTop),
+                        JS_THREAD_DATA(acx)->conservativeGC.enableCount);
                 JS_ASSERT(false);
                 abort();
             }
diff --git a/js/src/jsval.h b/js/src/jsval.h
index 540d1e9e6ce..a9d992057eb 100644
--- a/js/src/jsval.h
+++ b/js/src/jsval.h
@@ -150,7 +150,7 @@ JS_STATIC_ASSERT(sizeof(JSValueTag) == sizeof(uint32));
 
 JS_ENUM_HEADER(JSValueShiftedTag, uint64)
 {
-    JSVAL_SHIFTED_TAG_MAX_DOUBLE   = (((uint64)JSVAL_TAG_MAX_DOUBLE) << JSVAL_TAG_SHIFT),
+    JSVAL_SHIFTED_TAG_MAX_DOUBLE   = ((((uint64)JSVAL_TAG_MAX_DOUBLE) << JSVAL_TAG_SHIFT) | 0xFFFFFFFF),
     JSVAL_SHIFTED_TAG_INT32        = (((uint64)JSVAL_TAG_INT32)      << JSVAL_TAG_SHIFT),
     JSVAL_SHIFTED_TAG_UNDEFINED    = (((uint64)JSVAL_TAG_UNDEFINED)  << JSVAL_TAG_SHIFT),
     JSVAL_SHIFTED_TAG_STRING       = (((uint64)JSVAL_TAG_STRING)     << JSVAL_TAG_SHIFT),
@@ -207,7 +207,7 @@ typedef uint32 JSValueTag;
 #define JSVAL_TAG_OBJECT             (uint32)(JSVAL_TAG_MAX_DOUBLE | JSVAL_TYPE_OBJECT)
 
 typedef uint64 JSValueShiftedTag;
-#define JSVAL_SHIFTED_TAG_MAX_DOUBLE (((uint64)JSVAL_TAG_MAX_DOUBLE) << JSVAL_TAG_SHIFT)
+#define JSVAL_SHIFTED_TAG_MAX_DOUBLE ((((uint64)JSVAL_TAG_MAX_DOUBLE) << JSVAL_TAG_SHIFT) | 0xFFFFFFFF)
 #define JSVAL_SHIFTED_TAG_INT32      (((uint64)JSVAL_TAG_INT32)      << JSVAL_TAG_SHIFT)
 #define JSVAL_SHIFTED_TAG_UNDEFINED  (((uint64)JSVAL_TAG_UNDEFINED)  << JSVAL_TAG_SHIFT)
 #define JSVAL_SHIFTED_TAG_STRING     (((uint64)JSVAL_TAG_STRING)     << JSVAL_TAG_SHIFT)