diff --git a/ext/stringio/stringio.gemspec b/ext/stringio/stringio.gemspec
index 83654d5a93..77c9e79b7e 100644
--- a/ext/stringio/stringio.gemspec
+++ b/ext/stringio/stringio.gemspec
@@ -5,7 +5,7 @@
 
 source_version = ["", "ext/stringio/"].find do |dir|
   begin
-    File.open(File.join(__dir__, "#{dir}stringio.c")) {|f|
+    break File.open(File.join(__dir__, "#{dir}stringio.c")) {|f|
       f.gets("\n#define STRINGIO_VERSION ")
       f.gets[/\s*(".+")/, 1].undump
     }