diff --git a/core/dbt/parser/manifest.py b/core/dbt/parser/manifest.py
index 8cedd3e49ae..017ba02e678 100644
--- a/core/dbt/parser/manifest.py
+++ b/core/dbt/parser/manifest.py
@@ -159,7 +159,7 @@ def extended_msgpack_encoder(obj):
     elif type(obj) is datetime.datetime:
         datetime_bytes = msgpack.ExtType(2, obj.isoformat().encode())
         return datetime_bytes
-    elif type(obj) is agate:
+    elif isinstance(obj, agate.Table):
         agate_bytes = msgpack.ExtType(3, "".encode())
         return agate_bytes