1 files changed, 4 insertions, 0 deletions
diff --git a/src/string.c b/src/string.c
index 1c54ffa72..aa26b261c 100644
--- a/src/string.c
+++ b/src/string.c
@@ -781,6 +781,10 @@ num_index:
         }
       }
     default:
+      indx = mrb_Integer(mrb, indx);
+      if (mrb_nil_p(indx)) {
+        mrb_raise(mrb, E_TYPE_ERROR, "can't convert to Fixnum");
+      }
       idx = mrb_fixnum(indx);
       goto num_index;
   }