diff -r deda5b5160d2 Lib/test/test_pep263.py
--- a/Lib/test/test_pep263.py	Thu Dec 24 11:51:24 2015 +0200
+++ b/Lib/test/test_pep263.py	Sat Dec 26 11:59:07 2015 +0100
@@ -15,18 +15,19 @@ class PEP263Test(unittest.TestCase):
             '\\\xd0\x9f'
         )
 
+    def compile_exec(self, source):
+        code = compile(source, "dummy", "exec")
+        ns = {}
+        exec(code, ns)
+        return ns
+
     def test_compilestring(self):
         # see #1882
-        c = compile("\n# coding: utf-8\nu = u'\xc3\xb3'\n", "dummy", "exec")
-        d = {}
-        exec c in d
+        d = self.compile_exec("\n# coding: utf-8\nu = u'\xc3\xb3'\n")
         self.assertEqual(d['u'], u'\xf3')
 
-
     def test_issue3297(self):
-        c = compile("a, b = '\U0001010F', '\\U0001010F'", "dummy", "exec")
-        d = {}
-        exec(c, d)
+        d = self.compile_exec("a, b = '\U0001010F', '\\U0001010F'")
         self.assertEqual(d['a'], d['b'])
         self.assertEqual(len(d['a']), len(d['b']))
 
@@ -63,6 +64,13 @@ class PEP263Test(unittest.TestCase):
                                      'codec did not return a unicode'):
             from test import bad_coding3
 
+    def test_utf8_encoding(self):
+        # issue #25937: "utf8" cookie should behave like "utf-8"
+        for encoding in ('utf-8', 'utf8'):
+            source = "# coding: %s\ns = '\xd6\xd0\xce\xc4'" % encoding
+            ns = self.compile_exec(source)
+            self.assertEqual(ns['s'], '\xd6\xd0\xce\xc4')
+
 
 def test_main():
     test_support.run_unittest(PEP263Test)
diff -r deda5b5160d2 Parser/tokenizer.c
--- a/Parser/tokenizer.c	Thu Dec 24 11:51:24 2015 +0200
+++ b/Parser/tokenizer.c	Sat Dec 26 11:59:07 2015 +0100
@@ -193,6 +193,9 @@ get_normal_name(char *s)        /* for u
     if (strcmp(buf, "utf-8") == 0 ||
         strncmp(buf, "utf-8-", 6) == 0)
         return "utf-8";
+    else if (strcmp(buf, "utf8") == 0 ||
+        strncmp(buf, "utf8-", 6) == 0)
+        return "utf-8";
     else if (strcmp(buf, "latin-1") == 0 ||
              strcmp(buf, "iso-8859-1") == 0 ||
              strcmp(buf, "iso-latin-1") == 0 ||