diff --git a/include/dynamic-graph/signal.h b/include/dynamic-graph/signal.h
index 5d3c3bb2e201a8a4da6699afdab539ff2697b4dc..2eabff2e3d424ce3da73c5abcc799a4cf87bc6c4 100644
--- a/include/dynamic-graph/signal.h
+++ b/include/dynamic-graph/signal.h
@@ -107,6 +107,8 @@ public:
   }
 
 public:
+  /// checkCompatibility is used to get the object contained in the
+  /// signal. This used to verify if a dynamic cast is possible or not.
   virtual void checkCompatibility() { throw Tcopy; }
 
 private: