I found that default setup for conda.el to be annoying and not robust. Firstly, setting (conda-env-autoactivate-mode t) will output error everytime file. Apparently, from inspecting the code, this is how it is implemented! see below. (if conda-env-autoactivate-mode ;; already on, now switching off (advice-add 'switch-to-buffer :after #'conda--switch-buffer-auto-activate) (advice-remove 'switch-to-buffer #'conda--switch-buffer-auto-activate)) The error is (error "No such conda environment: %s" name) because input argument name has nil value when a file that is switched to don’t have environment.