1 files changed, 4 insertions, 0 deletions
diff --git a/msgpack/fallback.py b/msgpack/fallback.py
index 4540875..b27acb2 100644
--- a/msgpack/fallback.py
+++ b/msgpack/fallback.py
@@ -874,6 +874,10 @@ class Packer(object):
                 obj = self._default(obj)
                 default_used = 1
                 continue
+
+            if self._datetime and check(obj, _DateTime):
+                raise ValueError("Cannot serialize %r where tzinfo=None" % (obj,))
+
             raise TypeError("Cannot serialize %r" % (obj,))
 
     def pack(self, obj):