diff --git a/opencensus/trace/ext/flask/flask_middleware.py b/opencensus/trace/ext/flask/flask_middleware.py
index 8c9ddf1cc..2a3db49c5 100644
--- a/opencensus/trace/ext/flask/flask_middleware.py
+++ b/opencensus/trace/ext/flask/flask_middleware.py
@@ -260,18 +260,21 @@ def _teardown_request(self, exception):
 
             if exception is not None:
                 span = execution_context.get_current_span()
-                span.status = status.Status(
-                    code=code_pb2.UNKNOWN,
-                    message=str(exception)
-                )
-                # try attaching the stack trace to the span, only populated if
-                # the app has 'PROPAGATE_EXCEPTIONS', 'DEBUG', or 'TESTING'
-                # enabled
-                exc_type, _, exc_traceback = sys.exc_info()
-                if exc_traceback is not None:
-                    span.stack_trace = stack_trace.StackTrace.from_traceback(
-                        exc_traceback
+                if span is not None:
+                    span.status = status.Status(
+                        code=code_pb2.UNKNOWN,
+                        message=str(exception)
                     )
+                    # try attaching the stack trace to the span, only populated
+                    # if the app has 'PROPAGATE_EXCEPTIONS', 'DEBUG', or
+                    # 'TESTING' enabled
+                    exc_type, _, exc_traceback = sys.exc_info()
+                    if exc_traceback is not None:
+                        span.stack_trace = (
+                            stack_trace.StackTrace.from_traceback(
+                                exc_traceback
+                            )
+                        )
 
             tracer.end_span()
             tracer.finish()
diff --git a/tests/unit/trace/ext/flask/test_flask_middleware.py b/tests/unit/trace/ext/flask/test_flask_middleware.py
index fcf2f38cb..3f1aad18c 100644
--- a/tests/unit/trace/ext/flask/test_flask_middleware.py
+++ b/tests/unit/trace/ext/flask/test_flask_middleware.py
@@ -17,24 +17,32 @@
 
 import unittest
 
+from google.rpc import code_pb2
 import flask
 import mock
-from google.rpc import code_pb2
 
 from opencensus.trace import execution_context
-from opencensus.trace import span_data
 from opencensus.trace import span as span_module
+from opencensus.trace import span_data
 from opencensus.trace import stack_trace
 from opencensus.trace import status
-from opencensus.trace.exporters import print_exporter, stackdriver_exporter, \
-    zipkin_exporter, jaeger_exporter
+from opencensus.trace.blank_span import BlankSpan
+from opencensus.trace.exporters import jaeger_exporter
+from opencensus.trace.exporters import print_exporter
+from opencensus.trace.exporters import stackdriver_exporter
+from opencensus.trace.exporters import zipkin_exporter
 from opencensus.trace.exporters.ocagent import trace_exporter
 from opencensus.trace.ext.flask import flask_middleware
 from opencensus.trace.propagation import google_cloud_format
 from opencensus.trace.samplers import always_off, always_on, ProbabilitySampler
+from opencensus.trace.span_context import SpanContext
+from opencensus.trace.trace_options import TraceOptions
 from opencensus.trace.tracers import base
 from opencensus.trace.tracers import noop_tracer
-from opencensus.trace.blank_span import BlankSpan
+
+
+class FlaskTestException(Exception):
+    pass
 
 
 class TestFlaskMiddleware(unittest.TestCase):
@@ -53,7 +61,7 @@ def health_check():
 
         @app.route('/error')
         def error():
-            raise Exception('error')
+            raise FlaskTestException('error')
 
         return app
 
@@ -458,7 +466,7 @@ def test_teardown_include_exception_and_traceback(self):
         app = self.create_app()
         app.config['TESTING'] = True
         flask_middleware.FlaskMiddleware(app=app, exporter=mock_exporter)
-        with self.assertRaises(Exception):
+        with self.assertRaises(FlaskTestException):
             app.test_client().get('/error')
 
         exported_spandata = mock_exporter.export.call_args[0][0][0]
@@ -471,3 +479,24 @@ def test_teardown_include_exception_and_traceback(self):
         )
         self.assertIsNotNone(exported_spandata.stack_trace.stack_trace_hash_id)
         self.assertNotEqual(exported_spandata.stack_trace.stack_frames, [])
+
+    def test_teardown_include_exception_and_traceback_span_disabled(self):
+        sampler = always_off.AlwaysOffSampler()
+        app = self.create_app()
+        app.config['TESTING'] = True
+        middleware = flask_middleware.FlaskMiddleware(app=app, sampler=sampler)
+
+        # TODO: send trace options in header (#465)
+        original_method = middleware.propagator.from_headers
+
+        def nope(*args, **kwargs):
+            trace_options = TraceOptions()
+            trace_options.set_enabled(False)
+            return SpanContext(trace_options=trace_options)
+
+        middleware.propagator.from_headers = nope
+
+        with self.assertRaises(FlaskTestException):
+            app.test_client().get('/error')
+
+        middleware.propagator.from_headers = original_method