diff --git a/gtsam/inference/Factor.h b/gtsam/inference/Factor.h
index 9f6259681..71f1ef885 100644
--- a/gtsam/inference/Factor.h
+++ b/gtsam/inference/Factor.h
@@ -167,7 +167,7 @@ public:
   /// find
   const_iterator find(KeyType key) const { return std::find(begin(), end(), key); }
 
-  ///TODO: comment
+  /// Access the factor's involved variable keys
   const std::vector<KeyType>& keys() const { return keys_; }
 
   /** iterators */