diff --git a/src/gc.c b/src/gc.c
index 0ba6e3e76..cf6dd35ef 100644
--- a/src/gc.c
+++ b/src/gc.c
@@ -500,6 +500,7 @@ root_scan_phase(mrb_state *mrb)
   for (ci = mrb->cibase; ci <= mrb->ci; ci++) {
     if (!ci) continue;
     mrb_gc_mark( mrb, (struct RBasic*)ci->env);
+    mrb_gc_mark( mrb, (struct RBasic*)ci->proc);
   }
   /* mark irep pool */
   for (i=0; i<mrb->irep_len; i++) {