Igor, the following bug is present in different ways both in 5.3 and in 5.3-mwl89. https://bugs.launchpad.net/maria/+bug/725050 The crash in 5.3-mwl89 appeared after merging with the latest 5.3. The crash in 5.3 requires a rather artificial example, but it shows that there is some inconsistency in JOIN::keyuse in 5.3. Please look at the last bug comment - it contains a very small test case. I will ping you tonight after putting kids to sleep around 21:30. Timour