diff --git a/tool/test-coverage.rb b/tool/test-coverage.rb
index fef0e8567bbac1..055577feea6c88 100644
--- a/tool/test-coverage.rb
+++ b/tool/test-coverage.rb
@@ -11,6 +11,7 @@
   lib/rubygems/optparse
   tool
   test
+  spec
 ]
 
 def merge_coverage_data(res1, res2)