QAction::event: Ambiguous shortcut overload

[lansing]

I have a QPlainTextEdit and I wanted to add a shortcut to an action for toggling comment

pActionToggleComment->setShortcut(QKeySequence(Qt::CTRL + Qt::Key_Slash));

I got the error that the shortcut has been taken, how do I find out which action took it?
QAction::event: Ambiguous shortcut overload: Ctrl+/