diff --git a/PRESUBMIT.cfg b/PRESUBMIT.cfg
index 6e0e040..e66280f 100644
--- a/PRESUBMIT.cfg
+++ b/PRESUBMIT.cfg
@@ -8,3 +8,6 @@
 
 # Make sure RELEASE_NOTE field is present.
 release_note_field_check: true
+
+# Make sure cos_patch trailer is present.
+cos_patch_trailer_check: true