diff --git a/dsf/org.eclipse.cdt.dsf.ui/src/org/eclipse/cdt/dsf/debug/ui/contexts/DsfSuspendTrigger.java b/dsf/org.eclipse.cdt.dsf.ui/src/org/eclipse/cdt/dsf/debug/ui/contexts/DsfSuspendTrigger.java
index af47331e64b..116cbced995 100644
--- a/dsf/org.eclipse.cdt.dsf.ui/src/org/eclipse/cdt/dsf/debug/ui/contexts/DsfSuspendTrigger.java
+++ b/dsf/org.eclipse.cdt.dsf.ui/src/org/eclipse/cdt/dsf/debug/ui/contexts/DsfSuspendTrigger.java
@@ -100,9 +100,18 @@ public class DsfSuspendTrigger implements ISuspendTrigger {
     
     @ThreadSafe
     public void dispose() {
-        if (fEventListenerRegisterd) {
-            fSession.removeServiceEventListener(this);
+        try {
+            fSession.getExecutor().execute(new DsfRunnable() {
+                public void run() {
+                    if (fEventListenerRegisterd) {
+                        fSession.removeServiceEventListener(this);
+                    }
+                }
+            });
+        } catch (RejectedExecutionException e) {
+            // Session already gone.
         }
+            
         fServicesTracker.dispose();
         fDisposed = true;
     }
diff --git a/dsf/org.eclipse.cdt.dsf.ui/src/org/eclipse/cdt/dsf/debug/ui/viewmodel/SteppingController.java b/dsf/org.eclipse.cdt.dsf.ui/src/org/eclipse/cdt/dsf/debug/ui/viewmodel/SteppingController.java
index 6dcb37110c6..14ccb4df44e 100644
--- a/dsf/org.eclipse.cdt.dsf.ui/src/org/eclipse/cdt/dsf/debug/ui/viewmodel/SteppingController.java
+++ b/dsf/org.eclipse.cdt.dsf.ui/src/org/eclipse/cdt/dsf/debug/ui/viewmodel/SteppingController.java
@@ -16,6 +16,7 @@ import java.util.HashMap;
 import java.util.LinkedList;
 import java.util.List;
 import java.util.Map;
+import java.util.concurrent.RejectedExecutionException;
 import java.util.concurrent.ScheduledFuture;
 import java.util.concurrent.TimeUnit;
 
@@ -164,9 +165,17 @@ public final class SteppingController
     }
 
     public void dispose() {
-    	if (fRunControl != null) {
-    		getSession().removeServiceEventListener(this);
-    	}
+        try {
+            fSession.getExecutor().execute(new DsfRunnable() {
+                public void run() {
+                    if (fRunControl != null) {
+                        getSession().removeServiceEventListener(this);
+                    }
+                }
+            });
+        } catch (RejectedExecutionException e) {
+            // Session already gone.
+        }
     	
         IPreferenceStore store= DsfUIPlugin.getDefault().getPreferenceStore();
         store.removePropertyChangeListener(fPreferencesListener);
diff --git a/dsf/org.eclipse.cdt.dsf/src/org/eclipse/cdt/dsf/service/DsfSession.java b/dsf/org.eclipse.cdt.dsf/src/org/eclipse/cdt/dsf/service/DsfSession.java
index 78d25e7e310..563acb828f8 100644
--- a/dsf/org.eclipse.cdt.dsf/src/org/eclipse/cdt/dsf/service/DsfSession.java
+++ b/dsf/org.eclipse.cdt.dsf/src/org/eclipse/cdt/dsf/service/DsfSession.java
@@ -305,6 +305,8 @@ public class DsfSession
      * listener will receive events from 
      */
     public void addServiceEventListener(Object listener, Filter filter) {
+        assert getExecutor().isInExecutorThread();
+        
         ListenerEntry entry = new ListenerEntry(listener, filter);
         assert !fListeners.containsKey(entry);
         if (DEBUG_SESSION_LISTENERS) {
@@ -325,6 +327,8 @@ public class DsfSession
      * @param listener listener to remove
      */
     public void removeServiceEventListener(Object listener) {
+        assert getExecutor().isInExecutorThread();
+
         ListenerEntry entry = new ListenerEntry(listener, null);
         assert fListeners.containsKey(entry);
         if (DEBUG_SESSION_LISTENERS) {