diff -r ae69ebd41807 Lib/idlelib/IOBinding.py
--- a/Lib/idlelib/IOBinding.py	Fri Jan 03 15:52:22 2014 -0500
+++ b/Lib/idlelib/IOBinding.py	Sat Jan 04 10:35:59 2014 +0200
@@ -64,6 +64,7 @@
                             ### 'encoding' is used below in encode(), check!
 
 coding_re = re.compile(r'^[ \t\f]*#.*coding[:=][ \t]*([-\w.]+)', re.ASCII)
+blank_re = re.compile(r'^[ \t\f]*(?:[#\r\n]|$)', re.ASCII)
 
 def coding_spec(data):
     """Return the encoding declaration according to PEP 263.
@@ -93,6 +94,8 @@
         match = coding_re.match(line)
         if match is not None:
             break
+        if not blank_re.match(line):
+            return None
     else:
         return None
     name = match.group(1)
diff -r ae69ebd41807 Lib/lib2to3/pgen2/tokenize.py
--- a/Lib/lib2to3/pgen2/tokenize.py	Fri Jan 03 15:52:22 2014 -0500
+++ b/Lib/lib2to3/pgen2/tokenize.py	Sat Jan 04 10:35:59 2014 +0200
@@ -237,6 +237,7 @@
             toks_append(tokval)
 
 cookie_re = re.compile(r'^[ \t\f]*#.*coding[:=][ \t]*([-\w.]+)', re.ASCII)
+blank_re = re.compile(br'^[ \t\f]*(?:[#\r\n]|$)', re.ASCII)
 
 def _get_normal_name(orig_enc):
     """Imitates get_normal_name in tokenizer.c."""
@@ -309,6 +310,8 @@
     encoding = find_cookie(first)
     if encoding:
         return encoding, [first]
+    if not blank_re.match(first):
+        return default, [first]
 
     second = read_or_stop()
     if not second:
diff -r ae69ebd41807 Lib/test/test_source_encoding.py
--- a/Lib/test/test_source_encoding.py	Fri Jan 03 15:52:22 2014 -0500
+++ b/Lib/test/test_source_encoding.py	Sat Jan 04 10:35:59 2014 +0200
@@ -1,7 +1,8 @@
 # -*- coding: koi8-r -*-
 
 import unittest
-from test.support import TESTFN, unlink, unload
+from test.support import TESTFN, unlink, unload, captured_stdout
+from test.script_helper import assert_python_ok
 import importlib
 import os
 import sys
@@ -130,6 +131,50 @@
         self.assertTrue(c.exception.args[0].startswith(expected),
                         msg=c.exception.args[0])
 
+    def source_encoding_test(self, source, expected):
+        with captured_stdout() as out:
+            exec(source)
+        self.assertEqual(out.getvalue(), expected)
+
+        filename = TESTFN + '.py'
+        self.addCleanup(unlink, filename)
+        with open(filename, 'wb') as f:
+            f.write(source)
+        rc, out, err = assert_python_ok(filename)
+        self.assertEqual(out, expected.encode('ascii'))
+
+    def test_noncommented_first_line(self):
+        self.source_encoding_test(
+            ("print(ascii('\u00a31'), end=';')\n"
+             "# -*- coding: iso8859-15 -*-\n"
+             "print(ascii('\u20ac2'), end='')\n").encode('utf-8'),
+            r"'\xa31';'\u20ac2'")
+
+    def test_commented_first_line(self):
+        self.source_encoding_test(
+            ("#print(ascii('\u00a31'), end=';')\n"
+             "# -*- coding: iso8859-15 -*-\n"
+             "print(ascii('\u20ac2'), end='')\n").encode('utf-8'),
+            r"'\xe2\x82\xac2'")
+
+    def test_empty_first_line(self):
+        self.source_encoding_test(
+            ("\n"
+             "# -*- coding: iso8859-15 -*-\n"
+             "print(ascii('\u20ac2'), end='')\n").encode('utf-8'),
+            r"'\xe2\x82\xac2'")
+
+    def test_skip_first_line(self):
+        source = ("print(ascii('\u00a31'), end=';')\n"
+                  "# -*- coding: iso8859-15 -*-\n"
+                  "print(ascii('\u20ac2'), end='')\n").encode('utf-8')
+        filename = TESTFN + '.py'
+        self.addCleanup(unlink, filename)
+        with open(filename, 'wb') as f:
+            f.write(source)
+        rc, out, err = assert_python_ok('-x', filename)
+        self.assertEqual(out, br"'\xe2\x82\xac2'")
+
 
 if __name__ == "__main__":
     unittest.main()
diff -r ae69ebd41807 Lib/test/test_tokenize.py
--- a/Lib/test/test_tokenize.py	Fri Jan 03 15:52:22 2014 -0500
+++ b/Lib/test/test_tokenize.py	Sat Jan 04 10:35:59 2014 +0200
@@ -885,6 +885,39 @@
         readline = self.get_readline(lines)
         self.assertRaises(SyntaxError, detect_encoding, readline)
 
+    def test_cookie_second_line_noncommented_first_line(self):
+        lines = (
+            b"print('\xc2\xa3')\n",
+            b'# vim: set fileencoding=iso8859-15 :\n',
+            b"print('\xe2\x82\xac')\n"
+        )
+        encoding, consumed_lines = detect_encoding(self.get_readline(lines))
+        self.assertEqual(encoding, 'utf-8')
+        expected = [b"print('\xc2\xa3')\n"]
+        self.assertEqual(consumed_lines, expected)
+
+    def test_cookie_second_line_commented_first_line(self):
+        lines = (
+            b"#print('\xc2\xa3')\n",
+            b'# vim: set fileencoding=iso8859-15 :\n',
+            b"print('\xe2\x82\xac')\n"
+        )
+        encoding, consumed_lines = detect_encoding(self.get_readline(lines))
+        self.assertEqual(encoding, 'iso8859-15')
+        expected = [b"#print('\xc2\xa3')\n", b'# vim: set fileencoding=iso8859-15 :\n']
+        self.assertEqual(consumed_lines, expected)
+
+    def test_cookie_second_line_empty_first_line(self):
+        lines = (
+            b'\n',
+            b'# vim: set fileencoding=iso8859-15 :\n',
+            b"print('\xe2\x82\xac')\n"
+        )
+        encoding, consumed_lines = detect_encoding(self.get_readline(lines))
+        self.assertEqual(encoding, 'iso8859-15')
+        expected = [b'\n', b'# vim: set fileencoding=iso8859-15 :\n']
+        self.assertEqual(consumed_lines, expected)
+
     def test_latin1_normalization(self):
         # See get_normal_name() in tokenizer.c.
         encodings = ("latin-1", "iso-8859-1", "iso-latin-1", "latin-1-unix",
diff -r ae69ebd41807 Lib/tokenize.py
--- a/Lib/tokenize.py	Fri Jan 03 15:52:22 2014 -0500
+++ b/Lib/tokenize.py	Sat Jan 04 10:35:59 2014 +0200
@@ -32,6 +32,7 @@
 import collections
 from io import TextIOWrapper
 cookie_re = re.compile(r'^[ \t\f]*#.*coding[:=][ \t]*([-\w.]+)', re.ASCII)
+blank_re = re.compile(br'^[ \t\f]*(?:[#\r\n]|$)', re.ASCII)
 
 import token
 __all__ = token.__all__ + ["COMMENT", "tokenize", "detect_encoding",
@@ -409,6 +410,8 @@
     encoding = find_cookie(first)
     if encoding:
         return encoding, [first]
+    if not blank_re.match(first):
+        return default, [first]
 
     second = read_or_stop()
     if not second:
diff -r ae69ebd41807 Parser/tokenizer.c
--- a/Parser/tokenizer.c	Fri Jan 03 15:52:22 2014 -0500
+++ b/Parser/tokenizer.c	Sat Jan 04 10:35:59 2014 +0200
@@ -283,13 +283,27 @@
     char *cs;
     int r = 1;
 
-    if (tok->cont_line)
+    if (tok->cont_line) {
         /* It's a continuation line, so it can't be a coding spec. */
+        tok->read_coding_spec = 1;
         return 1;
+    }
     if (!get_coding_spec(line, &cs, size, tok))
         return 0;
-    if (!cs)
+    if (!cs) {
+        Py_ssize_t i;
+        for (i = 0; i < size; i++) {
+            if (line[i] == '#' || line[i] == '\n' || line[i] == '\r')
+                break;
+            if (line[i] != ' ' && line[i] != '\t' && line[i] != '\014') {
+                /* Stop checking coding spec after a line containing
+                 * anything except a comment. */
+                tok->read_coding_spec = 1;
+                break;
+            }
+        }
         return 1;
+    }
     tok->read_coding_spec = 1;
     if (tok->encoding == NULL) {
         assert(tok->decoding_state == STATE_RAW);
@@ -476,13 +490,17 @@
     _Py_IDENTIFIER(open);
     _Py_IDENTIFIER(readline);
     int fd;
+    long pos;
 
     io = PyImport_ImportModuleNoBlock("io");
     if (io == NULL)
         goto cleanup;
 
     fd = fileno(tok->fp);
-    if (lseek(fd, 0, SEEK_SET) == (off_t)-1) {
+    /* Due to buffering the file offset for fd can be different from the file
+     * position of tok->fp. */
+    pos = ftell(tok->fp);
+    if (pos == -1 || lseek(fd, (off_t)pos, SEEK_SET) == (off_t)-1) {
         PyErr_SetFromErrnoWithFilename(PyExc_OSError, NULL);
         goto cleanup;
     }
@@ -752,7 +770,7 @@
     if (newl[0]) {
         if (!check_coding_spec(str, newl[0] - str, tok, buf_setreadl))
             return error_ret(tok);
-        if (tok->enc == NULL && newl[1]) {
+        if (tok->enc == NULL && !tok->read_coding_spec && newl[1]) {
             if (!check_coding_spec(newl[0]+1, newl[1] - newl[0],
                                    tok, buf_setreadl))
                 return error_ret(tok);
diff -r ae69ebd41807 Tools/scripts/findnocoding.py
--- a/Tools/scripts/findnocoding.py	Fri Jan 03 15:52:22 2014 -0500
+++ b/Tools/scripts/findnocoding.py	Sat Jan 04 10:35:59 2014 +0200
@@ -33,6 +33,7 @@
 
 
 decl_re = re.compile(rb'^[ \t\f]*#.*coding[:=][ \t]*([-\w.]+)')
+blank_re = re.compile(rb'^[ \t\f]*(?:[#\r\n]|$)')
 
 def get_declaration(line):
     match = decl_re.match(line)
@@ -58,7 +59,8 @@
         line1 = infile.readline()
         line2 = infile.readline()
 
-        if get_declaration(line1) or get_declaration(line2):
+        if (get_declaration(line1) or
+            blank_re.match(line1) and get_declaration(line2)):
             # the file does have an encoding declaration, so trust it
             return False