diff --git a/py25/bacpypes/task.py b/py25/bacpypes/task.py
index 14adde4..f2eab6e 100755
--- a/py25/bacpypes/task.py
+++ b/py25/bacpypes/task.py
@@ -74,7 +74,11 @@ class _Task(DebugContents, Logging):
     def suspend_task(self):
         global _task_manager
 
-        _task_manager.suspend_task(self)
+        # pass along to the task manager
+        if not _task_manager:
+            _unscheduled_tasks.remove(self)
+        else:
+            _task_manager.suspend_task(self)
 
     def resume_task(self):
         global _task_manager
diff --git a/py27/bacpypes/task.py b/py27/bacpypes/task.py
index c212c83..73760eb 100755
--- a/py27/bacpypes/task.py
+++ b/py27/bacpypes/task.py
@@ -74,7 +74,11 @@ class _Task(DebugContents, Logging):
     def suspend_task(self):
         global _task_manager
 
-        _task_manager.suspend_task(self)
+        # pass along to the task manager
+        if not _task_manager:
+            _unscheduled_tasks.remove(self)
+        else:
+            _task_manager.suspend_task(self)
 
     def resume_task(self):
         global _task_manager
diff --git a/py34/bacpypes/task.py b/py34/bacpypes/task.py
index c212c83..73760eb 100755
--- a/py34/bacpypes/task.py
+++ b/py34/bacpypes/task.py
@@ -74,7 +74,11 @@ class _Task(DebugContents, Logging):
     def suspend_task(self):
         global _task_manager
 
-        _task_manager.suspend_task(self)
+        # pass along to the task manager
+        if not _task_manager:
+            _unscheduled_tasks.remove(self)
+        else:
+            _task_manager.suspend_task(self)
 
     def resume_task(self):
         global _task_manager