diff --git a/src/core/ev.c b/src/core/ev.c
index ac1d3568..76c8d315 100644
--- a/src/core/ev.c
+++ b/src/core/ev.c
@@ -465,6 +465,7 @@ const JanetAbstractType janet_stream_type = {
 /* Register a fiber to resume with value */
 void janet_schedule_signal(JanetFiber *fiber, Janet value, JanetSignal sig) {
     if (fiber->gc.flags & JANET_FIBER_EV_FLAG_CANCELED) return;
+    fiber->gc.flags |= JANET_FIBER_FLAG_ROOT;
     JanetTask t = { fiber, value, sig, ++fiber->sched_id };
     if (sig == JANET_SIGNAL_ERROR) fiber->gc.flags |= JANET_FIBER_EV_FLAG_CANCELED;
     janet_q_push(&janet_vm.spawn, &t, sizeof(t));
diff --git a/src/core/vm.c b/src/core/vm.c
index d43a4804..fb8c22f0 100644
--- a/src/core/vm.c
+++ b/src/core/vm.c
@@ -1338,8 +1338,9 @@ static JanetSignal janet_check_can_resume(JanetFiber *fiber, Janet *out, int is_
         *out = janet_cstringv("C stack recursed too deeply");
         return JANET_SIGNAL_ERROR;
     }
-    /* If a "task" fiber is trying to be used as a normal fiber, detect that. See bug #920. */
-    if (janet_vm.stackn > 0 && (fiber->gc.flags & JANET_FIBER_FLAG_ROOT)) {
+    /* If a "task" fiber is trying to be used as a normal fiber, detect that. See bug #920.
+     * Fibers must be marked as root fibers manually, or by the ev scheduler. */
+    if (janet_vm.fiber != NULL && (fiber->gc.flags & JANET_FIBER_FLAG_ROOT)) {
 #ifdef JANET_EV
         *out = janet_cstringv(is_cancel
                               ? "cannot cancel root fiber, use ev/cancel"
@@ -1351,9 +1352,6 @@ static JanetSignal janet_check_can_resume(JanetFiber *fiber, Janet *out, int is_
 #endif
         return JANET_SIGNAL_ERROR;
     }
-    if (janet_vm.stackn == 0) {
-        fiber->gc.flags |= JANET_FIBER_FLAG_ROOT;
-    }
     if (old_status == JANET_STATUS_ALIVE ||
             old_status == JANET_STATUS_DEAD ||
             (old_status >= JANET_STATUS_USER0 && old_status <= JANET_STATUS_USER4) ||