diff -r 3d1cdbd76fbe Lib/ctypes/test/test_bitfields.py
--- a/Lib/ctypes/test/test_bitfields.py	Tue Aug 16 22:28:23 2011 -0500
+++ b/Lib/ctypes/test/test_bitfields.py	Wed Aug 17 08:58:48 2011 -0700
@@ -240,5 +240,13 @@
 _anonymous_ = ["_"]
 _fields_ = [("_", X)]
 
+ def test_invalid_name(self):
+ # field name must be string
+ def declare_with_name(name):
+ class S(Structure):
+ _fields_ = [(name, c_int)]
+
+ self.assertRaises(TypeError, declare_with_name, b"x")
+
 if __name__ == "__main__":
 unittest.main()
diff -r 3d1cdbd76fbe Modules/_ctypes/stgdict.c
--- a/Modules/_ctypes/stgdict.c	Tue Aug 16 22:28:23 2011 -0500
+++ b/Modules/_ctypes/stgdict.c	Wed Aug 17 08:58:48 2011 -0700
@@ -480,10 +480,23 @@
 bitsize = 0;
 if (isStruct && !isPacked) {
 char *fieldfmt = dict->format ? dict->format : "B";
+ char *ptr = NULL;
+ Py_ssize_t len = 0; 
+ char *buf = NULL;
 char *fieldname = _PyUnicode_AsString(name);
- char *ptr;
- Py_ssize_t len = strlen(fieldname) + strlen(fieldfmt);
- char *buf = alloca(len + 2 + 1);
+
+ if (fieldname == NULL)
+ {
+ PyErr_Format(PyExc_TypeError,
+ "structure field name must be string not %s",
+ name->ob_type->tp_name);
+ 
+ Py_DECREF(pair);
+ return -1;
+ }
+
+ len = strlen(fieldname) + strlen(fieldfmt);
+ buf = alloca(len + 2 + 1);
 
 sprintf(buf, "%s:%s:", fieldfmt, fieldname);
 
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