diff --git a/packages/google-cloud-oslogin/src/v1beta/doc/google/protobuf/doc_field_mask.js b/packages/google-cloud-oslogin/src/v1beta/doc/google/protobuf/doc_field_mask.js
index c82c2b33949..d700752b7c6 100644
--- a/packages/google-cloud-oslogin/src/v1beta/doc/google/protobuf/doc_field_mask.js
+++ b/packages/google-cloud-oslogin/src/v1beta/doc/google/protobuf/doc_field_mask.js
@@ -218,6 +218,12 @@
  * Note that oneof type names ("test_oneof" in this case) cannot be used in
  * paths.
  *
+ * ## Field Mask Verification
+ *
+ * The implementation of any API method which has a FieldMask type field in the
+ * request should verify the included field paths, and return an
+ * `INVALID_ARGUMENT` error if any path is duplicated or unmappable.
+ *
  * @property {string[]} paths
  *   The set of field mask paths.
  *