diff -r 7efe1a5239e3 Lib/ctypes/test/test_structures.py
--- a/Lib/ctypes/test/test_structures.py	Fri Jun 17 11:13:03 2016 +0300
+++ b/Lib/ctypes/test/test_structures.py	Fri Jun 17 11:29:21 2016 +0300
@@ -227,10 +227,10 @@ class StructureTestCase(unittest.TestCas
 
     def test_conflicting_initializers(self):
         class POINT(Structure):
-            _fields_ = [("x", c_int), ("y", c_int)]
+            _fields_ = [("x", c_int), ("ÿ", c_int)]
         # conflicting positional and keyword args
         self.assertRaises(TypeError, POINT, 2, 3, x=4)
-        self.assertRaises(TypeError, POINT, 2, 3, y=4)
+        self.assertRaisesRegex(TypeError, "ÿ", POINT, 2, 3, ÿ=4)
 
         # too many initializers
         self.assertRaises(TypeError, POINT, 2, 3, 4)
diff -r 7efe1a5239e3 Modules/_ctypes/_ctypes.c
--- a/Modules/_ctypes/_ctypes.c	Fri Jun 17 11:13:03 2016 +0300
+++ b/Modules/_ctypes/_ctypes.c	Fri Jun 17 11:29:21 2016 +0300
@@ -4065,14 +4065,9 @@ static Py_ssize_t
         }
         val = PyTuple_GET_ITEM(args, i + index);
         if (kwds && PyDict_GetItem(kwds, name)) {
-            char *field = PyBytes_AsString(name);
-            if (field == NULL) {
-                PyErr_Clear();
-                field = "???";
-            }
             PyErr_Format(PyExc_TypeError,
-                         "duplicate values for field '%s'",
-                         field);
+                         "duplicate values for field %R",
+                         name);
             Py_DECREF(pair);
             Py_DECREF(name);
             return -1;