diff --git a/heat/engine/scheduler.py b/heat/engine/scheduler.py
index 528596f9c3..217a03de8d 100644
--- a/heat/engine/scheduler.py
+++ b/heat/engine/scheduler.py
@@ -20,7 +20,6 @@ from oslo_log import log as logging
 from oslo_utils import encodeutils
 from oslo_utils import excutils
 import six
-from six import reraise as raise_
 
 from heat.common.i18n import _
 from heat.common.i18n import _LI
@@ -421,47 +420,50 @@ class DependencyTaskGroup(object):
         raised_exceptions = []
         thrown_exceptions = []
 
-        while any(six.itervalues(self._runners)):
-            try:
-                for k, r in self._ready():
-                    r.start()
-                    if not r:
-                        del self._graph[k]
+        try:
+            while any(six.itervalues(self._runners)):
+                try:
+                    for k, r in self._ready():
+                        r.start()
+                        if not r:
+                            del self._graph[k]
 
-                if self._graph:
+                    if self._graph:
+                        try:
+                            yield
+                        except Exception:
+                            thrown_exceptions.append(sys.exc_info())
+                            raise
+
+                    for k, r in self._running():
+                        if r.step():
+                            del self._graph[k]
+                except Exception:
+                    exc_info = None
                     try:
-                        yield
-                    except Exception:
-                        thrown_exceptions.append(sys.exc_info())
-                        raise
+                        exc_info = sys.exc_info()
+                        if self.aggregate_exceptions:
+                            self._cancel_recursively(k, r)
+                        else:
+                            self.cancel_all(grace_period=self.error_wait_time)
+                        raised_exceptions.append(exc_info)
+                    finally:
+                        del exc_info
+                except:  # noqa
+                    with excutils.save_and_reraise_exception():
+                        self.cancel_all()
 
-                for k, r in self._running():
-                    if r.step():
-                        del self._graph[k]
-            except Exception:
-                exc_info = sys.exc_info()
-                if self.aggregate_exceptions:
-                    self._cancel_recursively(k, r)
-                else:
-                    self.cancel_all(grace_period=self.error_wait_time)
-                raised_exceptions.append(exc_info)
-                del exc_info
-            except:  # noqa
-                with excutils.save_and_reraise_exception():
-                    self.cancel_all()
-
-        if raised_exceptions:
-            try:
+            if raised_exceptions:
                 if self.aggregate_exceptions:
                     raise ExceptionGroup(v for t, v, tb in raised_exceptions)
                 else:
                     if thrown_exceptions:
-                        raise_(*thrown_exceptions[-1])
+                        six.reraise(*thrown_exceptions[-1])
                     else:
-                        raise_(*raised_exceptions[0])
-            finally:
-                del raised_exceptions
-                del thrown_exceptions
+                        six.reraise(*raised_exceptions[0])
+        finally:
+            del raised_exceptions
+            del thrown_exceptions
 
     def cancel_all(self, grace_period=None):
         if callable(grace_period):
@@ -478,7 +480,10 @@ class DependencyTaskGroup(object):
                 LOG.debug('Exception cancelling task: %s' % six.text_type(ex))
 
     def _cancel_recursively(self, key, runner):
-        runner.cancel()
+        try:
+            runner.cancel()
+        except Exception as ex:
+            LOG.debug('Exception cancelling task: %s' % six.text_type(ex))
         node = self._graph[key]
         for dependent_node in node.required_by():
             node_runner = self._runners[dependent_node]