diff --git a/src/tools/ntqmap.h b/src/tools/ntqmap.h
index c8d97fd5..3139e7fe 100644
--- a/src/tools/ntqmap.h
+++ b/src/tools/ntqmap.h
@@ -644,8 +644,12 @@ public:
 #endif
     ~TQMap()
     {
-	if ( sh->deref() )
-	    delete sh;
+	if ( sh ) {
+	    if ( sh->deref() ) {
+		delete sh;
+		sh = 0L;
+	    }
+	}
     }
     TQMap<Key,T>& operator= ( const TQMap<Key,T>& m );
 #ifndef QT_NO_STL