Strengthen the guard.  The code doesn't work well with subclasses.
diff --git a/Objects/unicodeobject.c b/Objects/unicodeobject.c
index 47e0933..7cc7037 100644
--- a/Objects/unicodeobject.c
+++ b/Objects/unicodeobject.c
@@ -8547,7 +8547,7 @@
         }
     } else {
         /* x must be a dict */
-        if (!PyDict_Check(x)) {
+        if (!PyDict_CheckExact(x)) {
             PyErr_SetString(PyExc_TypeError, "if you give only one argument "
                             "to maketrans it must be a dict");
             goto err;