diff --git a/tool/sync_default_gems.rb b/tool/sync_default_gems.rb
index e425965042..5f8a73448e 100755
--- a/tool/sync_default_gems.rb
+++ b/tool/sync_default_gems.rb
@@ -437,6 +437,7 @@ module SyncDefaultGems
       [^/]+ # top-level entries
       |\.git.*
       |bin/.*
+      |ext/.*\.java
       |rakelib/.*
       |test/(?:lib|fixtures)/.*
       |tool/.*