1 files changed, 4 insertions, 1 deletions
diff --git a/src/string.c b/src/string.c
index 2b1a27fee..aa26b261c 100644
--- a/src/string.c
+++ b/src/string.c
@@ -781,7 +781,10 @@ num_index:
         }
       }
     default:
-      if (mrb_nil_p(indx)) mrb_raise(mrb, E_TYPE_ERROR, "can't convert nil into Integer");
+      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;
   }