diff --git a/src/core/ev.c b/src/core/ev.c
index 14730fa9..395542a5 100644
--- a/src/core/ev.c
+++ b/src/core/ev.c
@@ -2369,6 +2369,7 @@ void janet_ev_default_threaded_callback(JanetEVGenericMessage return_value) {
         /* Clean up */
         switch (return_value.tag) {
             default:
+                break;
             case JANET_EV_TCTAG_STRINGF:
             case JANET_EV_TCTAG_ERR_STRINGF:
                 janet_free(return_value.argp);
@@ -2379,6 +2380,7 @@ void janet_ev_default_threaded_callback(JanetEVGenericMessage return_value) {
     if (janet_fiber_can_resume(return_value.fiber)) {
         switch (return_value.tag) {
             default:
+                break;
             case JANET_EV_TCTAG_NIL:
                 janet_schedule(return_value.fiber, janet_wrap_nil());
                 break;
@@ -2407,6 +2409,7 @@ void janet_ev_default_threaded_callback(JanetEVGenericMessage return_value) {
     /* Clean up */
     switch (return_value.tag) {
         default:
+            break;
         case JANET_EV_TCTAG_STRINGF:
         case JANET_EV_TCTAG_ERR_STRINGF:
             janet_free(return_value.argp);
diff --git a/src/core/os.c b/src/core/os.c
index 6c01693b..c8ef4277 100644
--- a/src/core/os.c
+++ b/src/core/os.c
@@ -1623,6 +1623,7 @@ JANET_CORE_FN(os_posix_chroot,
 static JanetEVGenericMessage os_shell_subr(JanetEVGenericMessage args) {
     int stat = system((const char *) args.argp);
     janet_free(args.argp);
+    args.argp = NULL;
     if (args.argi) {
         args.tag = JANET_EV_TCTAG_INTEGER;
     } else {