diff --git a/src/gui/panels/timeline-panel.hpp b/src/gui/panels/timeline-panel.hpp
index 90d7b8978..c1c29aee2 100644
--- a/src/gui/panels/timeline-panel.hpp
+++ b/src/gui/panels/timeline-panel.hpp
@@ -35,8 +35,10 @@
 #include "gui/widgets/timeline/timeline-zoom-scale.hpp"
 
 #include "lib/time/timevalue.hpp"
+#include "lib/util-coll.hpp"
 
 #include <memory>
+#include <map>
 
 using namespace gui::widgets;
 
@@ -178,6 +180,7 @@ private:
 
   std::map< weak_ptr<model::Sequence>
           , shared_ptr<widgets::timeline::TimelineState>
+          , ::util::WeakPtrComparator
           > 
     timelineStates;
   
diff --git a/src/gui/widgets/timeline/timeline-layout-helper.cpp b/src/gui/widgets/timeline/timeline-layout-helper.cpp
index 08afb5ce5..42cfaab4d 100644
--- a/src/gui/widgets/timeline/timeline-layout-helper.cpp
+++ b/src/gui/widgets/timeline/timeline-layout-helper.cpp
@@ -29,9 +29,13 @@
 
 #include <boost/foreach.hpp>
 #include <memory>
+#include <list>
 
 using std::pair;
+using std::list;
 using std::shared_ptr;
+using std::weak_ptr;
+using std::dynamic_pointer_cast;
 
 using namespace Gtk;
 using namespace lumiera;
diff --git a/src/lib/util-coll.hpp b/src/lib/util-coll.hpp
index e3246f433..123b5f75f 100644
--- a/src/lib/util-coll.hpp
+++ b/src/lib/util-coll.hpp
@@ -163,5 +163,19 @@ namespace util {
   
   
   
+  /* === generic container helpers === */
+  
+  struct WeakPtrComparator
+    {
+      template<typename T>
+      bool
+      operator() (std::weak_ptr<T> const& l, std::weak_ptr<T> const& r) const
+        {
+          return l.lock().get() < r.lock().get();
+        }
+    };
+  
+  
+  
 } // namespace util
 #endif /*UTIL_COLL_H*/
diff --git a/tests/core/proc/mobject/session/defs-manager-impl-test.cpp b/tests/core/proc/mobject/session/defs-manager-impl-test.cpp
index 3171728a8..01f6ffadc 100644
--- a/tests/core/proc/mobject/session/defs-manager-impl-test.cpp
+++ b/tests/core/proc/mobject/session/defs-manager-impl-test.cpp
@@ -65,7 +65,7 @@ namespace test    {
   bool
   find (const string& pID)
   {
-    return Session::current->defaults.search (Query<Pipe> ("pipe("+pID+")"));
+    return bool(Session::current->defaults.search (Query<Pipe> ("pipe("+pID+")")));
   }
   
   
diff --git a/tests/core/proc/mobject/session/defs-manager-test.cpp b/tests/core/proc/mobject/session/defs-manager-test.cpp
index 1a14abfa2..bdd357c62 100644
--- a/tests/core/proc/mobject/session/defs-manager-test.cpp
+++ b/tests/core/proc/mobject/session/defs-manager-test.cpp
@@ -65,7 +65,7 @@ namespace test    {
   bool
   find (Query<Pipe>& q)
   {
-    return Session::current->defaults.search (q);
+    return bool(Session::current->defaults.search (q));
   }