diff --git a/MANIFEST b/MANIFEST
index 9be3a0041f..7a999f353c 100644
--- a/MANIFEST
+++ b/MANIFEST
@@ -702,6 +702,7 @@ test/soap/marshal/test_marshal.rb
 test/soap/marshal/test_struct.rb
 test/soap/test_basetype.rb
 test/soap/test_soapelement.rb
+test/stringio/test_stringio.rb
 test/strscan/test_stringscanner.rb
 test/testunit/collector/test_dir.rb
 test/testunit/collector/test_objectspace.rb