diff --git a/pecan/core.py b/pecan/core.py
index 8155180..b6c09ff 100644
--- a/pecan/core.py
+++ b/pecan/core.py
@@ -371,10 +371,15 @@ class Pecan(object):
 
         # attempt to guess the content type based on the file extension
         if not request.pecan['content_type'] and '.' in path.split('/')[-1]:
-            path, extension = splitext(path)
-            request.pecan['extension'] = extension
+            new_path, extension = splitext(path)
+
             # preface with a letter to ensure compat for 2.5
-            request.pecan['content_type'] = guess_type('x' + extension)[0]
+            potential_type = guess_type('x' + extension)[0]
+
+            if potential_type is not None:
+                path = new_path
+                request.pecan['extension'] = extension
+                request.pecan['content_type'] = potential_type
 
         controller, remainder = self.route(self.root, path)
         cfg = _cfg(controller)
diff --git a/pecan/tests/test_base.py b/pecan/tests/test_base.py
index 13d1c94..ba495b8 100644
--- a/pecan/tests/test_base.py
+++ b/pecan/tests/test_base.py
@@ -863,7 +863,11 @@ class TestFileTypeExtensions(unittest.TestCase):
         class RootController(object):
             @expose(content_type=None)
             def _default(self, *args):
-                return request.pecan['extension']
+                ext = request.pecan.get('extension')
+                assert len(args) == 1
+                if ext:
+                    assert ext not in args[0]
+                return ext or ''
 
         return TestApp(Pecan(RootController()))
 
@@ -883,7 +887,7 @@ class TestFileTypeExtensions(unittest.TestCase):
         assert r.body == ''
 
     def test_multi_dot_extension(self):
-        r = self.app_.get('/gradient.js.js')
+        r = self.app_.get('/gradient.min.js')
         assert r.status_int == 200
         assert r.body == '.js'
 
@@ -907,6 +911,20 @@ class TestFileTypeExtensions(unittest.TestCase):
             r = app.get('/index.txt', expect_errors=True)
             assert r.status_int == 404
 
+    def test_unknown_file_extension(self):
+        class RootController(object):
+            @expose(content_type=None)
+            def _default(self, *args):
+                assert 'example:x.tiny' in args
+                assert 'extension' not in request.pecan
+                return 'SOME VALUE'
+
+        app = TestApp(Pecan(RootController()))
+
+        r = app.get('/example:x.tiny')
+        assert r.status_int == 200
+        assert r.body == 'SOME VALUE'
+
 
 class TestContentTypeByAcceptHeaders(unittest.TestCase):