diff --git a/oauth2_http/java/com/google/auth/oauth2/OAuth2Credentials.java b/oauth2_http/java/com/google/auth/oauth2/OAuth2Credentials.java
index 160596979..1b611bdcd 100644
--- a/oauth2_http/java/com/google/auth/oauth2/OAuth2Credentials.java
+++ b/oauth2_http/java/com/google/auth/oauth2/OAuth2Credentials.java
@@ -167,6 +167,11 @@ public void refresh() throws IOException {
     }
   }
 
+  /**
+   * Provide additional headers to return as request metadata.
+   *
+   * @return Map of additional headers.
+   */
   protected Map<String, List<String>> getAdditionalHeaders() {
     return EMPTY_EXTRA_HEADERS;
   }