diff --git a/copasi/math/CMathDependencyGraph.cpp b/copasi/math/CMathDependencyGraph.cpp
index fd5b241a1b..14eaf5def4 100644
--- a/copasi/math/CMathDependencyGraph.cpp
+++ b/copasi/math/CMathDependencyGraph.cpp
@@ -162,8 +162,24 @@ bool CMathDependencyGraph::getUpdateSequence(CCore::CUpdateSequence & updateSequ
 #endif // DEBUG_OUTPUT
     }
 
-  CObjectInterface::ObjectSet::const_iterator it = changedObjects.begin();
-  CObjectInterface::ObjectSet::const_iterator end = changedObjects.end();
+  CObjectInterface::ObjectSet::const_iterator it = requestedObjects.begin();
+  CObjectInterface::ObjectSet::const_iterator end = requestedObjects.end();
+  CObjectInterface::ObjectSet Prerequisites;
+
+  for (; it != end && success; ++it)
+    (*it)->appendPrerequisites(Prerequisites);
+
+  CObjectInterface::ObjectSet ChangedObjects(changedObjects);
+
+  it = Prerequisites.begin();
+  end = Prerequisites.end();
+
+  for (; it != end; ++it)
+    if ((*it)->getPrerequisites().empty())
+      ChangedObjects.insert(*it);
+
+  it = ChangedObjects.begin();
+  end = ChangedObjects.end();
 
   // Mark all nodes which are changed or need to be calculated
   for (; it != end && success; ++it)
diff --git a/copasi/math/CMathEvent.cpp b/copasi/math/CMathEvent.cpp
index 2f9afd8d26..3c86f0e797 100644
--- a/copasi/math/CMathEvent.cpp
+++ b/copasi/math/CMathEvent.cpp
@@ -1388,12 +1388,13 @@ void CMathEvent::createUpdateSequences()
   const CObjectInterface::ObjectSet & SimulationValues = mpContainer->getSimulationUpToDateObjects();
 
   CObjectInterface::ObjectSet Requested;
+
   Requested.insert(mpDelay);
   mpContainer->getTransientDependencies().getUpdateSequence(mDelaySequence, CCore::SimulationContext::Default, StateValues, Requested, SimulationValues);
 
   Requested.clear();
+
   CObjectInterface::ObjectSet EventTargets;
-  CObjectInterface::ObjectSet Changed(StateValues);
   CAssignment * pAssignment = mAssignments.array();
   CAssignment * pAssignmentEnd = pAssignment + mAssignments.size();
 
@@ -1401,16 +1402,6 @@ void CMathEvent::createUpdateSequences()
     {
       Requested.insert(pAssignment->getAssignment());
 
-      CObjectInterface::ObjectSet Prerequisites;
-      pAssignment->getAssignment()->appendPrerequisites(Prerequisites);
-
-      CObjectInterface::ObjectSet::const_iterator it = Prerequisites.begin();
-      CObjectInterface::ObjectSet::const_iterator end = Prerequisites.end();
-
-      for (; it != end; ++it)
-        if ((*it)->getPrerequisites().empty())
-          Changed.insert(*it);
-
       const CMathObject * pTarget = pAssignment->getTarget();
 
       if (pTarget == NULL) continue;
@@ -1433,7 +1424,7 @@ void CMathEvent::createUpdateSequences()
         }
     }
 
-  mpContainer->getTransientDependencies().getUpdateSequence(mTargetValuesSequence, CCore::SimulationContext::Default, Changed, Requested, SimulationValues);
+  mpContainer->getTransientDependencies().getUpdateSequence(mTargetValuesSequence, CCore::SimulationContext::Default, StateValues, Requested, SimulationValues);
 
   // We need to add the total mass of the moieties to the state values.
   CObjectInterface::ObjectSet ExtendedStateValues = StateValues;