--- a/js/src/jsgc.cpp
+++ b/js/src/jsgc.cpp
@@ -2768,16 +2768,25 @@ BeginMarkPhase(JSRuntime *rt)
      * to atoms that we would miss.
      */
     Zone *atomsZone = rt->atomsCompartment->zone();
 
     bool keepAtoms = false;
     for (ThreadDataIter iter(rt); !iter.done(); iter.next())
         keepAtoms |= iter->gcKeepAtoms;
 
+    /*
+     * We don't scan the stacks of exclusive threads, so we need to avoid
+     * collecting their objects in another way. The only GC thing pointers they
+     * have are to their exclusive compartment (which is not collected) or to
+     * the atoms compartment. Therefore, we avoid collecting the atoms
+     * compartment when exclusive threads are running.
+     */
+    keepAtoms |= rt->exclusiveThreadsPresent();
+
     if (atomsZone->isGCScheduled() && rt->gcIsFull && !keepAtoms) {
         JS_ASSERT(!atomsZone->isCollecting());
         atomsZone->setGCState(Zone::Mark);
     }
 
     /*
      * At the end of each incremental slice, we call prepareForIncrementalGC,
      * which marks objects in all arenas that we're currently allocating
@@ -4347,16 +4356,18 @@ IncrementalSafety
 gc::IsIncrementalGCSafe(JSRuntime *rt)
 {
     JS_ASSERT(!rt->mainThread.suppressGC);
 
     bool keepAtoms = false;
     for (ThreadDataIter iter(rt); !iter.done(); iter.next())
         keepAtoms |= iter->gcKeepAtoms;
 
+    keepAtoms |= rt->exclusiveThreadsPresent();
+
     if (keepAtoms)
         return IncrementalSafety::Unsafe("gcKeepAtoms set");
 
     if (!rt->gcIncrementalEnabled)
         return IncrementalSafety::Unsafe("incremental permanently disabled");
 
     return IncrementalSafety::Safe();
 }

--- a/js/src/vm/Runtime.h
+++ b/js/src/vm/Runtime.h
@@ -760,16 +760,24 @@ struct JSRuntime : public JS::shadow::Ru
 #if defined(JS_THREADSAFE) && defined(DEBUG)
         return (!numExclusiveThreads && mainThreadHasExclusiveAccess) ||
             exclusiveAccessOwner == PR_GetCurrentThread();
 #else
         return true;
 #endif
     }
 
+    bool exclusiveThreadsPresent() const {
+#ifdef JS_THREADSAFE
+        return numExclusiveThreads > 0;
+#else
+        return false;
+#endif
+    }
+
     /* Default compartment. */
     JSCompartment       *atomsCompartment;
 
     /* Embedders can use this zone however they wish. */
     JS::Zone            *systemZone;
 
     /* List of compartments and zones (protected by the GC lock). */
     js::ZoneVector      zones;