Hi! I haven't been able to make a reproducer for this, but for illustrative purposes, here is a code snippet that fails with -O2 on Guile 3.0.5 and later (excerpt from GNU Shepherd): (define (run-command socket-file action service args) "Perform ACTION with ARGS on SERVICE, and display the result. Connect to the daemon via SOCKET-FILE." (with-system-error-handling (let ((sock (open-connection socket-file)) (action* (if (and (eq? action 'detailed-status) (memq service '(root shepherd))) 'status action))) ;; Send the command. (write-command (shepherd-command action* service #:arguments args) sock) https://git.savannah.gnu.org/cgit/shepherd.git/tree/modules/shepherd/scripts/herd.scm#n124 At -O2, (eq? action 'detailed-status) evaluates to true no matter what symbol ACTION holds. Interestingly, adding (pk action*) between LET and WRITE-COMMAND gives the expected result and mitigates the problem(!). There are other issues that can be observed by running the Shepherd test suite (i.e. make -j4 check). With -O1 all pass.