diff --git a/test/test_YoutubeDL.py b/test/test_YoutubeDL.py
index df8994b84..1d7452744 100644
--- a/test/test_YoutubeDL.py
+++ b/test/test_YoutubeDL.py
@@ -242,6 +242,7 @@ def test_format_selection_video(self):
     def test_format_selection_string_ops(self):
         formats = [
             {'format_id': 'abc-cba', 'ext': 'mp4', 'url': TEST_URL},
+            {'format_id': 'zxc-cxz', 'ext': 'webm', 'url': TEST_URL},
         ]
         info_dict = _make_result(formats)
 
@@ -253,6 +254,11 @@ def test_format_selection_string_ops(self):
 
         # does not equal (!=)
         ydl = YDL({'format': '[format_id!=abc-cba]'})
+        ydl.process_ie_result(info_dict.copy())
+        downloaded = ydl.downloaded_info_dicts[0]
+        self.assertEqual(downloaded['format_id'], 'zxc-cxz')
+
+        ydl = YDL({'format': '[format_id!=abc-cba][format_id!=zxc-cxz]'})
         self.assertRaises(ExtractorError, ydl.process_ie_result, info_dict.copy())
 
         # starts with (^=)
@@ -262,7 +268,12 @@ def test_format_selection_string_ops(self):
         self.assertEqual(downloaded['format_id'], 'abc-cba')
 
         # does not start with (!^=)
-        ydl = YDL({'format': '[format_id!^=abc-cba]'})
+        ydl = YDL({'format': '[format_id!^=abc]'})
+        ydl.process_ie_result(info_dict.copy())
+        downloaded = ydl.downloaded_info_dicts[0]
+        self.assertEqual(downloaded['format_id'], 'zxc-cxz')
+
+        ydl = YDL({'format': '[format_id!^=abc][format_id!^=zxc]'})
         self.assertRaises(ExtractorError, ydl.process_ie_result, info_dict.copy())
 
         # ends with ($=)
@@ -272,16 +283,29 @@ def test_format_selection_string_ops(self):
         self.assertEqual(downloaded['format_id'], 'abc-cba')
 
         # does not end with (!$=)
-        ydl = YDL({'format': '[format_id!$=abc-cba]'})
+        ydl = YDL({'format': '[format_id!$=cba]'})
+        ydl.process_ie_result(info_dict.copy())
+        downloaded = ydl.downloaded_info_dicts[0]
+        self.assertEqual(downloaded['format_id'], 'zxc-cxz')
+
+        ydl = YDL({'format': '[format_id!$=cba][format_id!$=cxz]'})
         self.assertRaises(ExtractorError, ydl.process_ie_result, info_dict.copy())
 
         # contains (*=)
-        ydl = YDL({'format': '[format_id*=-]'})
+        ydl = YDL({'format': '[format_id*=bc-cb]'})
         ydl.process_ie_result(info_dict.copy())
         downloaded = ydl.downloaded_info_dicts[0]
         self.assertEqual(downloaded['format_id'], 'abc-cba')
 
         # does not contain (!*=)
+        ydl = YDL({'format': '[format_id!*=bc-cb]'})
+        ydl.process_ie_result(info_dict.copy())
+        downloaded = ydl.downloaded_info_dicts[0]
+        self.assertEqual(downloaded['format_id'], 'zxc-cxz')
+
+        ydl = YDL({'format': '[format_id!*=abc][format_id!*=zxc]'})
+        self.assertRaises(ExtractorError, ydl.process_ie_result, info_dict.copy())
+
         ydl = YDL({'format': '[format_id!*=-]'})
         self.assertRaises(ExtractorError, ydl.process_ie_result, info_dict.copy())
 
diff --git a/youtube_dl/YoutubeDL.py b/youtube_dl/YoutubeDL.py
index a827414dc..80ed8d7e5 100755
--- a/youtube_dl/YoutubeDL.py
+++ b/youtube_dl/YoutubeDL.py
@@ -1078,7 +1078,7 @@ def _build_format_filter(self, filter_spec):
                 comparison_value = m.group('value')
                 str_op = STR_OPERATORS[m.group('op')]
                 if m.group('negation'):
-                    op = lambda attr, value: not str_op
+                    op = lambda attr, value: not str_op(attr, value)
                 else:
                     op = str_op