diff -r b4ccf8e1fdba Lib/ctypes/test/test_bitfields.py
--- a/Lib/ctypes/test/test_bitfields.py	Tue Aug 16 22:26:48 2011 -0500
+++ b/Lib/ctypes/test/test_bitfields.py	Wed Aug 17 09:00:46 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, u"x\xe9")
+
 if __name__ == "__main__":
     unittest.main()
diff -r b4ccf8e1fdba Modules/_ctypes/stgdict.c
--- a/Modules/_ctypes/stgdict.c	Tue Aug 16 22:26:48 2011 -0500
+++ b/Modules/_ctypes/stgdict.c	Wed Aug 17 09:00:46 2011 -0700
@@ -492,10 +492,23 @@
             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 = PyString_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);