diff --git a/backends/Debugger.cs b/backends/Debugger.cs
index ad01d994..59ea0e96 100644
--- a/backends/Debugger.cs
+++ b/backends/Debugger.cs
@@ -269,14 +269,14 @@ protected virtual void Dispose (bool disposing)
 
 			// If this is a call to Dispose, dispose all managed resources.
 			if (disposing) {
-				if (thread_manager != null) {
-					thread_manager.Dispose ();
-					thread_manager = null;
-				}
 				if (symtab_manager != null) {
 					symtab_manager.Dispose ();
 					symtab_manager = null;
 				}
+				if (thread_manager != null) {
+					thread_manager.Dispose ();
+					thread_manager = null;
+				}
 				if (bfd_container != null) {
 					bfd_container.Dispose ();
 					bfd_container = null;
diff --git a/backends/Process.cs b/backends/Process.cs
index 4e927009..d0c68e4e 100644
--- a/backends/Process.cs
+++ b/backends/Process.cs
@@ -772,7 +772,10 @@ protected void check_disposed ()
 
 		protected virtual void DoDispose ()
 		{
-			engine.Dispose ();
+			if (engine != null) {
+				engine.Dispose ();
+				engine = null;
+			}
 		}
 
 		protected virtual void Dispose (bool disposing)
diff --git a/backends/SingleSteppingEngine.cs b/backends/SingleSteppingEngine.cs
index 85dac46c..db65ec03 100644
--- a/backends/SingleSteppingEngine.cs
+++ b/backends/SingleSteppingEngine.cs
@@ -1861,19 +1861,14 @@ private void check_disposed ()
 		protected virtual void Dispose (bool disposing)
 		{
 			// Check to see if Dispose has already been called.
-			lock (this) {
-				if (disposed)
-					return;
-
-				disposed = true;
-			}
-
 			// If this is a call to Dispose, dispose all managed resources.
 			if (disposing) {
 				if (inferior != null)
 					inferior.Kill ();
 				inferior = null;
 			}
+
+			disposed = true;
 		}
 
 		public void Dispose ()
diff --git a/backends/ThreadManager.cs b/backends/ThreadManager.cs
index a197bb15..9e25c34f 100644
--- a/backends/ThreadManager.cs
+++ b/backends/ThreadManager.cs
@@ -139,9 +139,11 @@ public void StartApplication (ProcessStart start)
 			this.start = start;
 
 			wait_thread = new Thread (new ThreadStart (start_wait_thread));
+			wait_thread.IsBackground = true;
 			wait_thread.Start ();
 
 			inferior_thread = new Thread (new ThreadStart (start_inferior));
+			inferior_thread.IsBackground = true;
 			inferior_thread.Start ();
 		}
 
@@ -668,7 +670,8 @@ protected virtual void DoDispose ()
 			thread_hash.Values.CopyTo (threads, 0);
 
 			for (int i = 0; i < threads.Length; i++)
-				threads [i].Kill ();
+				threads [i].Dispose ();
+			main_process.Dispose ();
 		}
 
 		private bool disposed = false;
diff --git a/classes/SymbolTableManager.cs b/classes/SymbolTableManager.cs
index 5afaa9e4..e6c38813 100644
--- a/classes/SymbolTableManager.cs
+++ b/classes/SymbolTableManager.cs
@@ -26,6 +26,7 @@ public SymbolTableManager ()
 			modules_loaded_event = new ManualResetEvent (true);
 			update_completed_event = new ManualResetEvent (true);
 			symtab_thread = new Thread (new ThreadStart (symtab_thread_start));
+			symtab_thread.IsBackground = true;
 			symtab_thread.Start ();
 		}