diff --git a/ext/stringio/stringio.c b/ext/stringio/stringio.c
index 363b363261..026a1faaa9 100644
--- a/ext/stringio/stringio.c
+++ b/ext/stringio/stringio.c
@@ -1376,6 +1376,7 @@ strio_read(int argc, VALUE *argv, VALUE self)
 	    StringValue(str);
 	    rb_str_modify(str);
 	}
+	/* fall through */
       case 1:
 	if (!NIL_P(argv[0])) {
 	    len = NUM2LONG(argv[0]);