diff --git a/src/vm.c b/src/vm.c
index 946d68323..afe0422f8 100644
--- a/src/vm.c
+++ b/src/vm.c
@@ -1207,6 +1207,7 @@ RETRY_TRY_BLOCK:
       else {
         mrb_value blk = regs[bidx];
         if (!mrb_nil_p(blk) && mrb_type(blk) != MRB_TT_PROC) {
+          ci->nregs = bidx+1;
           regs[bidx] = mrb_convert_type(mrb, blk, MRB_TT_PROC, "Proc", "to_proc");
         }
       }
@@ -1438,6 +1439,7 @@ RETRY_TRY_BLOCK:
         }
         blk = regs[bidx];
         if (!mrb_nil_p(blk) && mrb_type(blk) != MRB_TT_PROC) {
+          ci->nregs = bidx+1;
           regs[bidx] = mrb_convert_type(mrb, blk, MRB_TT_PROC, "Proc", "to_proc");
           ci = mrb->c->ci;
         }