diff -r 99ef4501205b Lib/test/test_pep263.py
--- a/Lib/test/test_pep263.py	Thu May 10 16:11:12 2012 +0100
+++ b/Lib/test/test_pep263.py	Wed May 16 08:49:48 2012 +0200
@@ -2,6 +2,7 @@
 
 import unittest
 from test import support
+from test.script_helper import assert_python_failure
 
 class PEP263Test(unittest.TestCase):
 
@@ -55,6 +56,23 @@ class PEP263Test(unittest.TestCase):
         # two bytes in common with the UTF-8 BOM
         self.assertRaises(SyntaxError, eval, b'\xef\xbb\x20')
 
+    def test_too_long_line(self):
+        # BUFSIZ at the best the maximum buffer size of any platform
+        # (e.g. Linux uses 8192)
+        BUFSIZ = 8192
+        code = '#' + repr('\u00A1' * BUFSIZ) + '\n'
+        filename = 'test.py'
+        self.addCleanup(support.unlink, filename)
+        with open(filename, 'w') as f:
+            f.write(code)
+        returncode, stdout, stderr = assert_python_failure(filename)
+        self.assertTrue(
+            stderr.startswith(
+                b'File "test.py", line 1\n'
+                b'SyntaxError: Line 1 of file test.py is longer than the internal buffer'),
+            "stderr=%a" % stderr)
+
+
 def test_main():
     support.run_unittest(PEP263Test)
 
diff -r 99ef4501205b Parser/tokenizer.c
--- a/Parser/tokenizer.c	Thu May 10 16:11:12 2012 +0100
+++ b/Parser/tokenizer.c	Wed May 16 08:49:48 2012 +0200
@@ -546,6 +546,7 @@ static char *
 decoding_fgets(char *s, int size, struct tok_state *tok)
 {
     char *line = NULL;
+    size_t len;
     int badchar = 0;
     for (;;) {
         if (tok->decoding_state == STATE_NORMAL) {
@@ -557,6 +558,15 @@ decoding_fgets(char *s, int size, struct
             /* We want a 'raw' read. */
             line = Py_UniversalNewlineFgets(s, size,
                                             tok->fp, NULL);
+            if (line != NULL) {
+                len = strlen(line);
+                if (1 < len && line[len-1] != '\n') {
+                    PyErr_Format(PyExc_SyntaxError,
+                            "Line %i of file %U is longer than the internal buffer (%i)",
+                            tok->lineno + 1, tok->filename, size);
+                    return error_ret(tok);
+                }
+            }
             break;
         } else {
             /* We have not yet determined the encoding.