diff --git a/src/corelib/thread/qmutex.h b/src/corelib/thread/qmutex.h
index 12987f16c30..607cc13a2f9 100644
--- a/src/corelib/thread/qmutex.h
+++ b/src/corelib/thread/qmutex.h
@@ -251,7 +251,7 @@ class Q_CORE_EXPORT QMutex
 public:
     enum RecursionMode { NonRecursive, Recursive };
 
-    inline explicit QMutex(RecursionMode mode = NonRecursive) Q_DECL_NOTHROW { Q_UNUSED(mode); }
+    inline Q_DECL_CONSTEXPR explicit QMutex(RecursionMode = NonRecursive) Q_DECL_NOTHROW { }
 
     inline void lock() Q_DECL_NOTHROW {}
     inline bool tryLock(int timeout = 0) Q_DECL_NOTHROW { Q_UNUSED(timeout); return true; }