diff --git a/src/corelib/statemachine/qstatemachine.h b/src/corelib/statemachine/qstatemachine.h
index cc9c8aa6528..6ea9fe49be8 100644
--- a/src/corelib/statemachine/qstatemachine.h
+++ b/src/corelib/statemachine/qstatemachine.h
@@ -114,7 +114,7 @@ public:
     };
 
     explicit QStateMachine(QObject *parent = 0);
-    QStateMachine(QState::ChildMode childMode, QObject *parent = 0);
+    explicit QStateMachine(QState::ChildMode childMode, QObject *parent = 0);
     ~QStateMachine();
 
     void addState(QAbstractState *state);