diff --git a/src/corelib/thread/qmutex.h b/src/corelib/thread/qmutex.h
index 407473c799..be62dc01d6 100644
--- a/src/corelib/thread/qmutex.h
+++ b/src/corelib/thread/qmutex.h
@@ -102,7 +102,10 @@ public:
     bool try_lock() noexcept { return tryLock(); }
 
 private:
-    inline bool fastTryLock() noexcept {
+    inline bool fastTryLock() noexcept
+    {
+        if (d_ptr.loadRelaxed() != nullptr)
+            return false;
         return d_ptr.testAndSetAcquire(nullptr, dummyLocked());
     }
     inline bool fastTryUnlock() noexcept {
diff --git a/src/corelib/thread/qreadwritelock.cpp b/src/corelib/thread/qreadwritelock.cpp
index 274d0ba7f8..32302b1e17 100644
--- a/src/corelib/thread/qreadwritelock.cpp
+++ b/src/corelib/thread/qreadwritelock.cpp
@@ -191,8 +191,8 @@ bool QReadWriteLock::tryLockForRead()
 bool QReadWriteLock::tryLockForRead(int timeout)
 {
     // Fast case: non contended:
-    QReadWriteLockPrivate *d;
-    if (d_ptr.testAndSetAcquire(nullptr, dummyLockedForRead, d))
+    QReadWriteLockPrivate *d = d_ptr.loadRelaxed();
+    if (d == nullptr && d_ptr.testAndSetAcquire(nullptr, dummyLockedForRead, d))
         return true;
 
     while (true) {
@@ -305,8 +305,8 @@ bool QReadWriteLock::tryLockForWrite()
 bool QReadWriteLock::tryLockForWrite(int timeout)
 {
     // Fast case: non contended:
-    QReadWriteLockPrivate *d;
-    if (d_ptr.testAndSetAcquire(nullptr, dummyLockedForWrite, d))
+    QReadWriteLockPrivate *d = d_ptr.loadRelaxed();
+    if (d == nullptr && d_ptr.testAndSetAcquire(nullptr, dummyLockedForWrite, d))
         return true;
 
     while (true) {