Index: vm_insnhelper.c
===================================================================
--- vm_insnhelper.c	(revision 29039)
+++ vm_insnhelper.c	(working copy)
@@ -58,6 +58,7 @@
     cfp->self = self;
     cfp->lfp = lfp;
     cfp->dfp = sp;
+    cfp->block_iseq = 0;
     cfp->proc = 0;
     cfp->me = 0;