diff --git a/pecan/debug.py b/pecan/debug.py
index eacd5b6..1c4a8c8 100644
--- a/pecan/debug.py
+++ b/pecan/debug.py
@@ -121,6 +121,9 @@ class DebugMiddleware(object):
         self.app = app
 
     def __call__(self, environ, start_response):
+        assert not environ['wsgi.multiprocess'], (
+            "The EvalException middleware is not usable in a "
+            "multi-process environment")
         try:
             return self.app(environ, start_response)
         except:
diff --git a/pecan/tests/test_commands.py b/pecan/tests/test_commands.py
index 5d390d8..d7bebd8 100644
--- a/pecan/tests/test_commands.py
+++ b/pecan/tests/test_commands.py
@@ -26,8 +26,11 @@ class TestCommandRunner(unittest.TestCase):
     def test_run(self):
         from pecan.commands import CommandRunner
         runner = CommandRunner()
-        with self.assertRaises(RuntimeError):
-            runner.run(['serve', 'missing_file.py'])
+        self.assertRaises(
+            RuntimeError,
+            runner.run,
+            ['serve', 'missing_file.py']
+        )
 
 
 class TestCreateCommand(unittest.TestCase):
diff --git a/pecan/tests/test_debug.py b/pecan/tests/test_debug.py
index 468ae0a..c5cbc6e 100644
--- a/pecan/tests/test_debug.py
+++ b/pecan/tests/test_debug.py
@@ -23,3 +23,25 @@ class TestDebugMiddleware(TestCase):
         r = self.app.get('/error', expect_errors=True)
         assert r.status_int == 400
         assert 'AssertionError' in r.body
+
+    def test_middleware_complains_in_multi_process_environment(self):
+
+        class MultiProcessApp(object):
+
+            def __init__(self, app):
+                self.app = app
+
+            def __call__(self, environ, start_response):
+                environ['wsgi.multiprocess'] = True
+                return self.app(environ, start_response)
+
+        def conditional_error_app(environ, start_response):
+            start_response("200 OK", [('Content-type', 'text/plain')])
+            return ['Hello, World!']
+
+        app = TestApp(MultiProcessApp(DebugMiddleware(conditional_error_app)))
+        self.assertRaises(
+            AssertionError, 
+            app.get,
+            '/'
+        )