A subclass of QFileSystemModel might override columnCount to return a value smalller than QFileSystemModelPrivate::NumColumns. In that case, constructing the bottomRight index for the dataChange signal would fail if we create it for column NumColumns - 1, and result in undefined behavior where the topLeft and bottomRight indices do not have the same parent. So ask for the columnCount of the parent index explicitly to construct the bottomRight index. The assert can be triggered via the "filesystemexplorer" example in qtdeclarative, which overrides columnCount to always return 1. As a drive-by name the variables correctly, bottom and top where mixed up. Pick-to: 6.5 Fixes: QTBUG-110632 Change-Id: I8a635ec733348d1eda2037c156ac0f7b09a2183d Reviewed-by: Mitch Curtis <mitch.curtis@qt.io>