diff --git a/src/optiondialog.cpp b/src/optiondialog.cpp
index d05ce79cfe74e17eb407762f5a22284dff3d551b..f7e073fa782f12415a38780d9dfbcb5ca7279fe5 100644
--- a/src/optiondialog.cpp
+++ b/src/optiondialog.cpp
@@ -603,7 +603,7 @@ void OptionDialog::buttonClicked( QAbstractButton *button ) {
 }
 
 void OptionDialog::helpRequested() {
-    KHelpClient::invokeHelp( QStringLiteral( "kdiff3/index.html" ), QString::null );
+    KHelpClient::invokeHelp( QStringLiteral( "kdiff3/index.html" ), QString());
 }
 
 OptionDialog::~OptionDialog( void ) {