diff --git a/Lib/ctypes/test/test_arrays.py b/Lib/ctypes/test/test_arrays.py
index 4ed566b48e..5990906eae 100644
--- a/Lib/ctypes/test/test_arrays.py
+++ b/Lib/ctypes/test/test_arrays.py
@@ -181,5 +181,28 @@ class ArrayTestCase(unittest.TestCase):
                 _type_ = c_int
                 _length_ = 1.87
 
+    def test_bad_length(self):
+        from _testcapi import LONG_MAX
+
+        with self.assertRaises(ValueError):
+            class T(Array):
+                _type_ = c_int
+                _length_ = -1 << 1000
+        with self.assertRaises(ValueError):
+            class T(Array):
+                _type_ = c_int
+                _length_ = -1
+        class T(Array):
+            _type_ = c_int
+            _length_ = 0
+        with self.assertRaises(OverflowError):
+            class T(Array):
+                _type_ = c_int
+                _length_ = LONG_MAX + 1
+        with self.assertRaises(OverflowError):
+            class T(Array):
+                _type_ = c_int
+                _length_ = 1 << 1000
+
 if __name__ == '__main__':
     unittest.main()
diff --git a/Modules/_ctypes/_ctypes.c b/Modules/_ctypes/_ctypes.c
index 9d42109b51..8143633529 100644
--- a/Modules/_ctypes/_ctypes.c
+++ b/Modules/_ctypes/_ctypes.c
@@ -1349,9 +1349,19 @@ PyCArrayType_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
         goto error;
     }
     length = PyLong_AsLongAndOverflow(length_attr, &overflow);
-    if (overflow) {
-        PyErr_SetString(PyExc_OverflowError,
-                        "The '_length_' attribute is too large");
+    /* PyLong_Check(length_attr) is true, so it is guaranteed that
+       no error occurred in PyLong_AsLongAndOverflow. */
+    assert(!(length == -1 && PyErr_Occurred()));
+    if (overflow || length < 0) {
+        if (overflow == 1) {
+            PyErr_SetString(PyExc_OverflowError,
+                            "The '_length_' attribute is too large");
+        }
+        else {
+            assert(overflow == -1 || length < 0);
+            PyErr_SetString(PyExc_ValueError,
+                            "The '_length_' attribute must be non-negative");
+        }
         Py_DECREF(length_attr);
         goto error;
     }