The button on the combo box that shows or hides the list is known in the Qt source as the Arrow. I don't see how it is possible to override the handling of the arrow being clicked when the popup is visible. When the list is visible the QComboBox isn't the active widget. It's something called a QComboBoxPrivate that doesn't appear to be a child of the QComboBox. The mouse event you'd have to handle goes to the QComboBoxPrivate.