diff --git a/dom/workers/WorkerPrivate.cpp b/dom/workers/WorkerPrivate.cpp
index eebcc140a429..02480caedb41 100644
--- a/dom/workers/WorkerPrivate.cpp
+++ b/dom/workers/WorkerPrivate.cpp
@@ -4262,9 +4262,10 @@ WorkerPrivate::GarbageCollectInternal(JSContext* aCx, bool aShrinking,
 {
   AssertIsOnWorkerThread();
 
-  if (aCollectChildren) {
+  if (aShrinking || aCollectChildren) {
     JSRuntime* rt = JS_GetRuntime(aCx);
     JS::PrepareForFullGC(rt);
+
     if (aShrinking) {
       JS::ShrinkingGC(rt, JS::gcreason::DOM_WORKER);
     }
@@ -4273,10 +4274,6 @@ WorkerPrivate::GarbageCollectInternal(JSContext* aCx, bool aShrinking,
     }
   }
   else {
-    // If aCollectChildren is false then it means this collection request was
-    // not generated by the main thread. At the moment only the periodic GC
-    // timer can end up here, so rather than force a collection let the JS
-    // engine decide if we need one.
     JS_MaybeGC(aCx);
   }
 
diff --git a/js/src/vm/Runtime.cpp b/js/src/vm/Runtime.cpp
index 06fe91c92814..b83b6be3234d 100644
--- a/js/src/vm/Runtime.cpp
+++ b/js/src/vm/Runtime.cpp
@@ -206,6 +206,7 @@ JSRuntime::setGCMaxMallocBytes(size_t value)
      * mean that value.
      */
     gcMaxMallocBytes = (ptrdiff_t(value) >= 0) ? value : size_t(-1) >> 1;
+    resetGCMallocBytes();
     for (ZonesIter zone(this); !zone.done(); zone.next())
         zone->setGCMaxMallocBytes(value);
 }