--- a/js/src/jsgc.cpp
+++ b/js/src/jsgc.cpp
@@ -1955,16 +1955,20 @@ js::TriggerZoneGC(Zone *zone, JS::gcreas
      * If parallel threads are running, wait till they
      * are stopped to trigger GC.
      */
     if (InParallelSection()) {
         ForkJoinSlice::Current()->requestZoneGC(zone, reason);
         return;
     }
 
+    /* Zones in use by a thread with an exclusive context can't be collected. */
+    if (zone->usedByExclusiveThread)
+        return;
+
     JSRuntime *rt = zone->runtimeFromMainThread();
 
     /* Don't trigger GCs when allocating under the operation callback lock. */
     if (rt->currentThreadOwnsOperationCallbackLock())
         return;
 
     if (rt->isHeapBusy())
         return;