diff --git a/CMakeLists.txt b/CMakeLists.txt
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -66,17 +66,17 @@
     #        (performance warning)
     # C4996: 'function': was declared deprecated
   ELSE()
-    SET(CXX_WARNING "-Wall -W")
+    SET(CXX_WARNING "-Wall")
   ENDIF()
 ENDIF()
 SET(LEMON_CXX_WARNING_FLAGS ${CXX_WARNING} CACHE STRING "LEMON warning flags.")
 
 SET(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${LEMON_CXX_WARNING_FLAGS}")
 
-SET( CMAKE_CXX_FLAGS_MAINTAINER "-Werror -ggdb" CACHE STRING
+SET( CMAKE_CXX_FLAGS_MAINTAINER "-Werror -ggdb -O0" CACHE STRING
     "Flags used by the C++ compiler during maintainer builds."
     FORCE )
-SET( CMAKE_C_FLAGS_MAINTAINER "-Werror" CACHE STRING
+SET( CMAKE_C_FLAGS_MAINTAINER "-Werror -O0" CACHE STRING
     "Flags used by the C compiler during maintainer builds."
     FORCE )
 SET( CMAKE_EXE_LINKER_FLAGS_MAINTAINER
diff --git a/lemon/bfs.h b/lemon/bfs.h
--- a/lemon/bfs.h
+++ b/lemon/bfs.h
@@ -1247,6 +1247,7 @@
         visitor.examine(arc);
       }
       _Visitor& visitor;
+      Constraints() {}
     };
   };
 #endif
diff --git a/lemon/concepts/graph_components.h b/lemon/concepts/graph_components.h
--- a/lemon/concepts/graph_components.h
+++ b/lemon/concepts/graph_components.h
@@ -115,6 +115,7 @@
 
         const _GraphItem &ia;
         const _GraphItem &ib;
+        Constraints() {}
       };
     };
 
@@ -174,6 +175,7 @@
         }
 
         const _Digraph& digraph;
+        Constraints() {}
       };
     };
 
@@ -290,6 +292,7 @@
         }
 
         const _Graph& graph;
+      Constraints() {}
       };
 
     };
@@ -369,6 +372,7 @@
         }
 
         const _Digraph& digraph;
+        Constraints() {}
       };
     };
 
@@ -421,6 +425,7 @@
         }
 
         const _Graph& graph;
+        Constraints() {}
       };
     };
 
@@ -498,6 +503,7 @@
           bi = it2;
         }
         const GR& g;
+        Constraints() {}
       };
     };
 
@@ -586,6 +592,7 @@
         }
         const Base& node;
         const GR& graph;
+        Constraints() {}
       };
     };
 
@@ -762,6 +769,7 @@
         }
 
         const _Digraph& digraph;
+        Constraints() {}
       };
     };
 
@@ -886,6 +894,7 @@
         }
 
         const _Graph& graph;
+        Constraints() {}
       };
     };
 
@@ -943,6 +952,7 @@
         }
 
         const _Digraph& digraph;
+        Constraints() {}
       };
     };
 
@@ -984,6 +994,7 @@
         }
 
         const _Graph& graph;
+        Constraints() {}
       };
     };
 
@@ -1061,6 +1072,7 @@
         const _Map &m;
         const GR &g;
         const typename GraphMap::Value &t;
+        Constraints() {}
       };
 
     };
@@ -1199,6 +1211,7 @@
         }
 
         const _Digraph& digraph;
+        Constraints() {}
       };
     };
 
@@ -1284,6 +1297,7 @@
         }
 
         const _Graph& graph;
+        Constraints() {}
       };
     };
 
@@ -1328,6 +1342,7 @@
         }
 
         _Digraph& digraph;
+        Constraints() {}
       };
     };
 
@@ -1372,6 +1387,7 @@
         }
 
         _Graph& graph;
+        Constraints() {}
       };
     };
 
@@ -1411,6 +1427,7 @@
         }
 
         _Digraph& digraph;
+        Constraints() {}
       };
     };
 
@@ -1450,6 +1467,7 @@
         }
 
         _Graph& graph;
+        Constraints() {}
       };
     };
 
@@ -1478,6 +1496,7 @@
         }
 
         _Digraph& digraph;
+        Constraints() {}
       };
     };
 
@@ -1506,6 +1525,7 @@
         }
 
         _Graph& graph;
+        Constraints() {}
       };
     };
 
diff --git a/lemon/concepts/heap.h b/lemon/concepts/heap.h
--- a/lemon/concepts/heap.h
+++ b/lemon/concepts/heap.h
@@ -252,6 +252,7 @@
 
         _Heap& heap;
         ItemIntMap& map;
+        Constraints() {}
       };
     };
 
diff --git a/lemon/concepts/maps.h b/lemon/concepts/maps.h
--- a/lemon/concepts/maps.h
+++ b/lemon/concepts/maps.h
@@ -68,6 +68,7 @@
         const Key& key;
         const typename _ReadMap::Key& own_key;
         const _ReadMap& m;
+        Constraints() {}
       };
 
     };
@@ -109,6 +110,7 @@
         const typename _WriteMap::Key& own_key;
         const typename _WriteMap::Value& own_val;
         _WriteMap& m;
+        Constraints() {}
       };
     };
 
@@ -129,7 +131,8 @@
 
       /// Returns the value associated with the given key.
       Value operator[](const Key &) const {
-        return *static_cast<Value *>(0);
+        Value *r = 0;
+        return *r;
       }
 
       /// Sets the value associated with the given key.
@@ -169,12 +172,14 @@
 
       /// Returns a reference to the value associated with the given key.
       Reference operator[](const Key &) {
-        return *static_cast<Value *>(0);
+        Value *r = 0;
+        return *r;
       }
 
       /// Returns a const reference to the value associated with the given key.
       ConstReference operator[](const Key &) const {
-        return *static_cast<Value *>(0);
+        Value *r = 0;
+        return *r;
       }
 
       /// Sets the value associated with the given key.
@@ -205,6 +210,7 @@
         typename _ReferenceMap::Reference own_ref;
         typename _ReferenceMap::ConstReference own_cref;
         _ReferenceMap& m;
+        Constraints() {}
       };
     };
 
diff --git a/lemon/concepts/path.h b/lemon/concepts/path.h
--- a/lemon/concepts/path.h
+++ b/lemon/concepts/path.h
@@ -159,6 +159,7 @@
           ignore_unused_variable_warning(ed);
         }
         _Path& p;
+        PathDumperConstraints() {}
       };
 
       template <typename _Digraph, typename _Path>
@@ -184,6 +185,7 @@
           ignore_unused_variable_warning(ed);
         }
         _Path& p;
+        PathDumperConstraints() {}
       };
 
     }
diff --git a/lemon/dfs.h b/lemon/dfs.h
--- a/lemon/dfs.h
+++ b/lemon/dfs.h
@@ -1191,6 +1191,7 @@
         visitor.backtrack(arc);
       }
       _Visitor& visitor;
+      Constraints() {}
     };
   };
 #endif