diff --git a/lemon/preflow.h b/lemon/preflow.h
--- a/lemon/preflow.h
+++ b/lemon/preflow.h
@@ -113,6 +113,9 @@
   /// the maximum flow value and the minimum cut is obtained. The
   /// second phase constructs a feasible maximum flow on each arc.
   ///
+  /// \warning This implementation cannot handle infinite or very large
+  /// capacities (e.g. the maximum value of \c CAP::Value).
+  ///
   /// \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>".