diff --git a/lemon/preflow.h b/lemon/preflow.h
--- a/lemon/preflow.h
+++ b/lemon/preflow.h
@@ -119,6 +119,11 @@
   /// \tparam GR The type of the digraph the algorithm runs on.
   /// \tparam CAP The type of the capacity map. The default map
   /// type is \ref concepts::Digraph::ArcMap "GR::ArcMap<int>".
+  /// \tparam TR The traits class that defines various types used by the
+  /// algorithm. By default, it is \ref PreflowDefaultTraits
+  /// "PreflowDefaultTraits<GR, CAP>".
+  /// In most cases, this parameter should not be set directly,
+  /// consider to use the named template parameters instead.
 #ifdef DOXYGEN
   template <typename GR, typename CAP, typename TR>
 #else