diff --git a/src/corelib/thread/qmutex_p.h b/src/corelib/thread/qmutex_p.h
index 565de31ca0..66d902d1c3 100644
--- a/src/corelib/thread/qmutex_p.h
+++ b/src/corelib/thread/qmutex_p.h
@@ -23,6 +23,8 @@
 #include <QtCore/qatomic.h>
 #include <QtCore/qdeadlinetimer.h>
 
+#include "qplatformdefs.h" // _POSIX_VERSION
+
 #if defined(Q_OS_MAC)
 # include <mach/semaphore.h>
 #elif defined(Q_OS_UNIX)