diff --git a/graphene/types/union.py b/graphene/types/union.py
index e05d7882..38e4a0a8 100644
--- a/graphene/types/union.py
+++ b/graphene/types/union.py
@@ -39,7 +39,7 @@ class Union(UnmountedType, BaseType):
             )
 
     Meta:
-        types (Iterable[graphene.ObjectType)]: Required. Collection of types that may be returned
+        types (Iterable[graphene.ObjectType]): Required. Collection of types that may be returned
             by this Union for the graphQL schema.
         name (optional, str): the name of the GraphQL type (must be unique in schema). Defaults to class
             name.