1 files changed, 4 insertions, 1 deletions
diff --git a/Lib/multiprocessing/reduction.py b/Lib/multiprocessing/reduction.py
index 7f65947379f..deca19ccad7 100644
--- a/Lib/multiprocessing/reduction.py
+++ b/Lib/multiprocessing/reduction.py
@@ -165,7 +165,10 @@ else:
                 if len(cmsg_data) % a.itemsize != 0:
                     raise ValueError
                 a.frombytes(cmsg_data)
-                assert len(a) % 256 == msg[0]
+                if len(a) % 256 != msg[0]:
+                    raise AssertionError(
+                        "Len is {0:n} but msg[0] is {1!r}".format(
+                            len(a), msg[0]))
                 return list(a)
         except (ValueError, IndexError):
             pass