diff --git a/dom/workers/MessageEventRunnable.cpp b/dom/workers/MessageEventRunnable.cpp
index b96e3b2f324d..c81c21e13acf 100644
--- a/dom/workers/MessageEventRunnable.cpp
+++ b/dom/workers/MessageEventRunnable.cpp
@@ -61,7 +61,12 @@ bool MessageEventRunnable::DispatchDOMEvent(JSContext* aCx,
         MarkerTracingType::START);
   }
 
-  Read(parent, aCx, &messageData, rv);
+  JS::CloneDataPolicy cloneDataPolicy;
+  // The target of a worker postMessage cannot change while the message is
+  // in-flight, so SAB status was checked at sending-time, and does not need to
+  // be checked when deserializing.
+  cloneDataPolicy.allowSharedMemory();
+  Read(parent, aCx, &messageData, cloneDataPolicy, rv);
 
   if (isTimelineRecording) {
     end = MakeUnique<WorkerTimelineMarker>(