Issue #16431: Also fix the opposite direction.

Lib/test/test_decimal.py

@@ -2052,6 +2052,10 @@ class UsabilityTest(unittest.TestCase):
         self.assertIs(type(b), MyDecimal)
         self.assertEqual(a, b)
 
+        c = Decimal(b)
+        self.assertIs(type(c), Decimal)
+        self.assertEqual(a, c)
+
     def test_implicit_context(self):
         Decimal = self.decimal.Decimal
         getcontext = self.decimal.getcontext

Modules/_decimal/_decimal.c

@@ -2345,7 +2345,7 @@ PyDecType_FromDecimalExact(PyTypeObject *type, PyObject *v, PyObject *context)
     PyObject *dec;
     uint32_t status = 0;
 
-    if (type == &PyDec_Type) {
+    if (type == Py_TYPE(v)) {
         Py_INCREF(v);
         return v;
     }