--- a/js/src/jsgc.cpp
+++ b/js/src/jsgc.cpp
@@ -2150,16 +2150,17 @@ gc_root_traversal(JSTracer *trc, const R
 
     if (ptr && !trc->runtime->gcCurrentCompartment) {
         /*
          * Use conservative machinery to find if ptr is a valid GC thing.
          * We only do this during global GCs, to preserve the invariant
          * that mark callbacks are not in place during compartment GCs.
          */
         JSTracer checker;
+        JS_ASSERT(trc->runtime == trc->context->runtime);
         JS_TracerInit(&checker, trc->context, EmptyMarkCallback);
         ConservativeGCTest test = MarkIfGCThingWord(&checker, reinterpret_cast<uintptr_t>(ptr));
         if (test != CGCT_VALID && entry.value.name) {
             fprintf(stderr,
 "JS API usage error: the address passed to JS_AddNamedRoot currently holds an\n"
 "invalid gcthing.  This is usually caused by a missing call to JS_RemoveRoot.\n"
 "The root's name is \"%s\".\n",
                     entry.value.name);
@@ -3492,16 +3493,17 @@ IncrementalGCSlice(JSContext *cx, int64_
     if (rt->gcIncrementalState == MARK) {
         gcstats::AutoPhase ap(rt->gcStats, gcstats::PHASE_MARK);
         SliceBudget sliceBudget(budget);
 
         /* If we needed delayed marking for gray roots, then collect until done. */
         if (!rt->gcMarker.hasBufferedGrayRoots())
             sliceBudget.reset();
 
+        rt->gcMarker.context = cx;
         bool finished = rt->gcMarker.drainMarkStack(sliceBudget);
 
         for (GCCompartmentsIter c(rt); !c.done(); c.next()) {
             c->barrierMarker_.context = cx;
             finished &= c->barrierMarker_.drainMarkStack(sliceBudget);
             c->barrierMarker_.context = NULL;
         }