diff --git a/Lib/encodings/__init__.py b/Lib/encodings/__init__.py
index ddd5afd..4b37d33 100644
--- a/Lib/encodings/__init__.py
+++ b/Lib/encodings/__init__.py
@@ -61,7 +61,8 @@
         if c.isalnum() or c == '.':
             if punct and chars:
                 chars.append('_')
-            chars.append(c)
+            if c.isascii():
+                chars.append(c)
             punct = False
         else:
             punct = True
diff --git a/Lib/test/test_codecs.py b/Lib/test/test_codecs.py
index ddf4e08..09ceef7 100644
--- a/Lib/test/test_codecs.py
+++ b/Lib/test/test_codecs.py
@@ -3417,7 +3417,7 @@
 
 class CodecNameNormalizationTest(unittest.TestCase):
     """Test codec name normalization"""
-    def test_normalized_encoding(self):
+    def test_codecs_lookup(self):
         FOUND = (1, 2, 3, 4)
         NOT_FOUND = (None, None, None, None)
         def search_function(encoding):
@@ -3439,6 +3439,18 @@
         self.assertEqual(NOT_FOUND, codecs.lookup('BBB.8'))
         self.assertEqual(NOT_FOUND, codecs.lookup('a\xe9\u20ac-8'))
 
+    def test_encodings_normalize_encoding(self):
+        # encodings.normalize_encoding() ignores non-ASCII characters.
+        normalize = encodings.normalize_encoding
+        self.assertEqual(normalize('utf_8'), 'utf_8')
+        self.assertEqual(normalize('utf\xE9\u20AC\U0010ffff-8'), 'utf_8')
+        self.assertEqual(normalize('utf   8'), 'utf_8')
+        # encodings.normalize_encoding() doesn't convert
+        # characters to lower case.
+        self.assertEqual(normalize('UTF 8'), 'UTF_8')
+        self.assertEqual(normalize('utf.8'), 'utf.8')
+        self.assertEqual(normalize('utf...8'), 'utf...8')
+
 
 if __name__ == "__main__":
     unittest.main()