diff --git a/lemon/concepts/heap.h b/lemon/concepts/heap.h
--- a/lemon/concepts/heap.h
+++ b/lemon/concepts/heap.h
@@ -71,9 +71,9 @@
       /// The item-int map must be initialized in such way that it assigns
       /// \c PRE_HEAP (<tt>-1</tt>) to any element to be put in the heap.
       enum State {
-        IN_HEAP = 0,    ///< The "in heap" state constant.
-        PRE_HEAP = -1,  ///< The "pre heap" state constant.
-        POST_HEAP = -2  ///< The "post heap" state constant.
+        IN_HEAP = 0,    ///< = 0. The "in heap" state constant.
+        PRE_HEAP = -1,  ///< = -1. The "pre heap" state constant.
+        POST_HEAP = -2  ///< = -2. The "post heap" state constant.
       };
 
       /// \brief The constructor.