Hi Alain, you are correct. The command does not work on macOS Catalina. The problem is that “Set Master File” uses CocoaDialog. Unfortunately CocoaDialog is still a 32-bit executable and the latest version of macOS does not support 32-bit software any more. For more information, please take a look here: https://github.com/textmate/bundle-support.tmbundle/issues/31. If you want to set a master file I would recommend using a `.tm_properties` properties file for now. For example, if your main `.tex` file is called `Master.tex`, then create a new document with the content TM_LATEX_MASTER = "$CWD/Thesis.tex” and store it as `.tm_properties` at the root of your LaTeX project. For more information about this feature, please take a look at section `2.3.1` of the LaTeX Bundle documentation. The documentation is available in TextMate under “Bundles” → “LaTeX” → “Help”. You can also access it online [here](https://github.com/textmate/latex.tmbundle/blob/master/Support/help/H…. Kind regards, René