diff --git a/src/concurrent/qtconcurrentthreadengine.cpp b/src/concurrent/qtconcurrentthreadengine.cpp
index 3293c49507d..cf424912b37 100644
--- a/src/concurrent/qtconcurrentthreadengine.cpp
+++ b/src/concurrent/qtconcurrentthreadengine.cpp
@@ -322,10 +322,13 @@ void ThreadEngineBase::run() // implements QRunnable.
 
 void ThreadEngineBase::handleException(const QException &exception)
 {
-    if (futureInterface)
+    if (futureInterface) {
         futureInterface->reportException(exception);
-    else if (!exceptionStore.hasException())
-        exceptionStore.setException(exception);
+    } else {
+        QMutexLocker lock(&mutex);
+        if (!exceptionStore.hasException())
+            exceptionStore.setException(exception);
+    }
 }
 #endif
 
diff --git a/src/concurrent/qtconcurrentthreadengine.h b/src/concurrent/qtconcurrentthreadengine.h
index af413707e49..b7be48d6125 100644
--- a/src/concurrent/qtconcurrentthreadengine.h
+++ b/src/concurrent/qtconcurrentthreadengine.h
@@ -121,6 +121,7 @@ protected:
     QThreadPool *threadPool;
     ThreadEngineBarrier barrier;
     QtPrivate::ExceptionStore exceptionStore;
+    QBasicMutex mutex;
 };