diff --git a/src/core/ev.c b/src/core/ev.c
index e5576fcc..8b1abe6d 100644
--- a/src/core/ev.c
+++ b/src/core/ev.c
@@ -2031,33 +2031,35 @@ void janet_ev_default_threaded_callback(JanetEVGenericMessage return_value) {
     if (return_value.fiber == NULL) {
         return;
     }
-    switch (return_value.tag) {
-        default:
-        case JANET_EV_TCTAG_NIL:
-            janet_schedule(return_value.fiber, janet_wrap_nil());
-            break;
-        case JANET_EV_TCTAG_INTEGER:
-            janet_schedule(return_value.fiber, janet_wrap_integer(return_value.argi));
-            break;
-        case JANET_EV_TCTAG_STRING:
-        case JANET_EV_TCTAG_STRINGF:
-            janet_schedule(return_value.fiber, janet_cstringv((const char *) return_value.argp));
-            if (return_value.tag == JANET_EV_TCTAG_STRINGF) janet_free(return_value.argp);
-            break;
-        case JANET_EV_TCTAG_KEYWORD:
-            janet_schedule(return_value.fiber, janet_ckeywordv((const char *) return_value.argp));
-            break;
-        case JANET_EV_TCTAG_ERR_STRING:
-        case JANET_EV_TCTAG_ERR_STRINGF:
-            janet_cancel(return_value.fiber, janet_cstringv((const char *) return_value.argp));
-            if (return_value.tag == JANET_EV_TCTAG_STRINGF) janet_free(return_value.argp);
-            break;
-        case JANET_EV_TCTAG_ERR_KEYWORD:
-            janet_cancel(return_value.fiber, janet_ckeywordv((const char *) return_value.argp));
-            break;
-        case JANET_EV_TCTAG_BOOLEAN:
-            janet_schedule(return_value.fiber, janet_wrap_boolean(return_value.argi));
-            break;
+    if (janet_fiber_can_resume(return_value.fiber)) {
+        switch (return_value.tag) {
+            default:
+            case JANET_EV_TCTAG_NIL:
+                janet_schedule(return_value.fiber, janet_wrap_nil());
+                break;
+            case JANET_EV_TCTAG_INTEGER:
+                janet_schedule(return_value.fiber, janet_wrap_integer(return_value.argi));
+                break;
+            case JANET_EV_TCTAG_STRING:
+            case JANET_EV_TCTAG_STRINGF:
+                janet_schedule(return_value.fiber, janet_cstringv((const char *) return_value.argp));
+                if (return_value.tag == JANET_EV_TCTAG_STRINGF) janet_free(return_value.argp);
+                break;
+            case JANET_EV_TCTAG_KEYWORD:
+                janet_schedule(return_value.fiber, janet_ckeywordv((const char *) return_value.argp));
+                break;
+            case JANET_EV_TCTAG_ERR_STRING:
+            case JANET_EV_TCTAG_ERR_STRINGF:
+                janet_cancel(return_value.fiber, janet_cstringv((const char *) return_value.argp));
+                if (return_value.tag == JANET_EV_TCTAG_STRINGF) janet_free(return_value.argp);
+                break;
+            case JANET_EV_TCTAG_ERR_KEYWORD:
+                janet_cancel(return_value.fiber, janet_ckeywordv((const char *) return_value.argp));
+                break;
+            case JANET_EV_TCTAG_BOOLEAN:
+                janet_schedule(return_value.fiber, janet_wrap_boolean(return_value.argi));
+                break;
+        }
     }
     janet_gcunroot(janet_wrap_fiber(return_value.fiber));
 }
diff --git a/src/core/os.c b/src/core/os.c
index a3ee2fe2..488001ee 100644
--- a/src/core/os.c
+++ b/src/core/os.c
@@ -529,7 +529,9 @@ static void janet_proc_wait_cb(JanetEVGenericMessage args) {
             JanetString s = janet_formatc("command failed with non-zero exit code %d", status);
             janet_cancel(args.fiber, janet_wrap_string(s));
         } else {
-            janet_schedule(args.fiber, janet_wrap_integer(status));
+            if (janet_fiber_can_resume(args.fiber)) {
+                janet_schedule(args.fiber, janet_wrap_integer(status));
+            }
         }
     }
 }
diff --git a/src/core/symcache.c b/src/core/symcache.c
index e1d9aeab..841bfbd9 100644
--- a/src/core/symcache.c
+++ b/src/core/symcache.c
@@ -233,6 +233,7 @@ const uint8_t *janet_symbol_gen(void) {
     head->length = sizeof(janet_vm.gensym_counter) - 1;
     head->hash = hash;
     sym = (uint8_t *)(head->data);
+    sym[head->length] = 0;
     memcpy(sym, janet_vm.gensym_counter, sizeof(janet_vm.gensym_counter));
     janet_symcache_put((const uint8_t *)sym, bucket);
     return (const uint8_t *)sym;