diff --git a/Lib/ctypes/test/test_structures.py b/Lib/ctypes/test/test_structures.py
index f9a1109..3005e82 100644
--- a/Lib/ctypes/test/test_structures.py
+++ b/Lib/ctypes/test/test_structures.py
@@ -215,6 +215,15 @@
         # too long
         self.assertRaises(ValueError, Person, "1234567", 5)
 
+    def test_conflicting_initializers(self):
+        class POINT(Structure):
+            _fields_ = [("x", c_int), ("y", c_int)]
+        # conflicting positional and keyword args
+        self.assertRaises(TypeError, POINT, 2, 3, x=4)
+        self.assertRaises(TypeError, POINT, 2, 3, y=4)
+
+        # Should this raise TypeError instead?
+        self.assertRaises(ValueError, POINT, 2, 3, 4)
 
     def test_keyword_initializers(self):
         class POINT(Structure):
diff --git a/Misc/NEWS b/Misc/NEWS
index 0a7d00c..29bd3dd 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -364,6 +364,9 @@
 Library
 -------
 
+- Issue #1831: ctypes now raises a TypeError if conflicting positional
+  and named arguments are passed to a Structure or Union initializer.
+
 - Convert the internal ctypes array type cache to a WeakValueDict so
   that array types do not live longer than needed.
 
diff --git a/Modules/_ctypes/_ctypes.c b/Modules/_ctypes/_ctypes.c
index 1ff8e12..8c66194 100644
--- a/Modules/_ctypes/_ctypes.c
+++ b/Modules/_ctypes/_ctypes.c
@@ -3578,6 +3578,21 @@
 				return IBUG("_fields_[i][0] failed");
 			}
 
+			if (kwds && PyDict_GetItem(kwds, name)) {
+				char *field = PyString_AsString(name);
+				if (field == NULL) {
+					PyErr_Clear();
+					field = "???";
+				}
+				PyErr_Format(PyExc_TypeError,
+					     "duplicate values for field %s",
+					     field);
+				Py_DECREF(pair);
+				Py_DECREF(name);
+				Py_DECREF(fields);
+				return -1;
+			}
+
 			val = PyTuple_GET_ITEM(args, i);
 			if (-1 == PyObject_SetAttr(self, name, val)) {
 				Py_DECREF(pair);