--- Coro/Coro/State.xs	2014/03/04 06:13:24	1.442
+++ Coro/Coro/State.xs	2014/03/06 06:40:32	1.443
@@ -2251,6 +2251,9 @@
     {
       struct coro *self = SvSTATE_current;
 
+      if (!self)
+        croak ("Coro::cancel called outside of thread content,");
+
       /* otherwise we cancel directly, purely for speed reasons
        * unfortunately, this requires some magic trickery, as
        * somebody else could cancel us, so we have to fight the cancellation.