Use the new Py_ARRAY_LENGTH macro
diff --git a/Objects/longobject.c b/Objects/longobject.c
index 85b3353..43e5f01 100644
--- a/Objects/longobject.c
+++ b/Objects/longobject.c
@@ -2444,8 +2444,7 @@
                     break;
                 }
     }
-    assert(1 <= x_size &&
-           x_size <= (Py_ssize_t)(sizeof(x_digits)/sizeof(digit)));
+    assert(1 <= x_size && x_size <= (Py_ssize_t)Py_ARRAY_LENGTH(x_digits));
 
     /* Round, and convert to double. */
     x_digits[0] += half_even_correction[x_digits[0] & 7];