diff --git a/sys/src/cmd/gs/src/zcontext.c b/sys/src/cmd/gs/src/zcontext.c
index 6919f288c..c1ca1526f 100644
--- a/sys/src/cmd/gs/src/zcontext.c
+++ b/sys/src/cmd/gs/src/zcontext.c
@@ -953,6 +953,7 @@ zlock(i_ctx_t *i_ctx_p)
 	return_error(e_VMerror);
     plock->holder_index = 0;
     plock->waiting.head_index = plock->waiting.tail_index = 0;
+    plock->scheduler = NULL;
     push(1);
     make_istruct(op, a_all, plock);
     return 0;