diff --git a/docker-compose.yaml b/docker-compose.yaml
index ca39394..19049c9 100644
--- a/docker-compose.yaml
+++ b/docker-compose.yaml
@@ -26,7 +26,7 @@ services:
   dev:
     <<: *base
     image: hiku-dev
-    
+
   docs:
     <<: *base
     image: hiku-docs
@@ -41,23 +41,23 @@ services:
   examples-federation:
     <<: *examples-base
     command: python3 examples/graphql_federation.py
-    
+
   examples-federation-v2:
     <<: *examples-base
     command: python3 examples/graphql_federation_v2.py
-  
+
   examples-flask:
     <<: *examples-base
-    command: python3 examples/graphql_flask.py  
-              
+    command: python3 examples/graphql_flask.py
+
   examples-aiohttp:
     <<: *examples-base
     command: python3 examples/graphql_aiohttp.py
-    
+
   federation-compatibility-server:
     <<: *examples-base
     entrypoint: pdm run python examples/federation-compatibility/server.py
-    
+
   test-base: &test-base
     <<: *base
     image: hiku-tests
diff --git a/hiku/federation/sdl.py b/hiku/federation/sdl.py
index e6bbec6..b6752f9 100644
--- a/hiku/federation/sdl.py
+++ b/hiku/federation/sdl.py
@@ -39,6 +39,7 @@
 from hiku.scalar import ScalarMeta
 from hiku.types import (
     EnumRefMeta,
+    UnionRefMeta,
     IDMeta,
     IntegerMeta,
     MappingMeta,
@@ -101,6 +102,8 @@ def _encode(
             return val.__type_name__
         elif isinstance(val, EnumRefMeta):
             return val.__type_name__
+        elif isinstance(val, UnionRefMeta):
+            return val.__type_name__
         elif isinstance(val, ScalarMeta):
             return val.__type_name__
         elif isinstance(val, IntegerMeta):
diff --git a/lets.yaml b/lets.yaml
index 612d856..9fd48c2 100644
--- a/lets.yaml
+++ b/lets.yaml
@@ -38,7 +38,7 @@ commands:
     description: Build docker image for test
     depends: [_build-base]
     cmd: docker build -t hiku-tests -f Dockerfile --target tests .
-    
+
   _build-dev:
     description: Build docker image for dev
     depends: [_build-base]
@@ -53,7 +53,7 @@ commands:
     description: Run tests
     depends: [_build-tests]
     cmd: [docker-compose, run, --rm, test]
-    
+
   test-tox:
     description: Run tests using tox
     depends: [_build-tests]
@@ -68,7 +68,7 @@ commands:
     description: Run flake8
     depends: [_build-dev]
     cmd: docker-compose run --rm dev pdm run flake
-    
+
   black:
     description: Run flake8
     depends: [_build-dev]
@@ -83,7 +83,7 @@ commands:
     description: Run federation app from examples
     depends: [_build-examples]
     cmd: docker-compose up examples-federation
-    
+
   examples-federation-v2:
     description: Run federation 2 app from examples
     depends: [_build-examples]
diff --git a/tests/test_federation/test_sdl_v1.py b/tests/test_federation/test_sdl_v1.py
index 528349b..b129f1d 100644
--- a/tests/test_federation/test_sdl_v1.py
+++ b/tests/test_federation/test_sdl_v1.py
@@ -5,7 +5,8 @@
     Field,
     Link,
     Option,
-    Root, Union,
+    Root,
+    Union,
 )
 from hiku.types import (
     Record,
@@ -13,6 +14,7 @@
     String,
     TypeRef,
     Optional,
+    UnionRef,
 )
 from hiku.graph import apply
 
@@ -61,6 +63,15 @@ def execute(graph, query_string):
                 Option('id', Integer),
             ],
         ),
+        Link(
+            'bucket',
+            UnionRef['Bucket'],
+            link_resolver,
+            requires=None,
+            options=[
+                Option('id', Integer),
+            ],
+        ),
     ]),
 ], data_types={
     'Status': Record[{
@@ -97,6 +108,7 @@ def execute(graph, query_string):
 
     extend type Query {
       order(id: Int!): Order
+      bucket(id: Int!): Bucket!
     }
     
     scalar Any
diff --git a/tests/test_federation/test_sdl_v2.py b/tests/test_federation/test_sdl_v2.py
index d1afe36..7cfe939 100644
--- a/tests/test_federation/test_sdl_v2.py
+++ b/tests/test_federation/test_sdl_v2.py
@@ -8,14 +8,18 @@
     Field,
     Link,
     Option,
-    Root, Union,
+    Root,
+    Union,
 )
 from hiku.types import (
-    Boolean, EnumRef, Record,
+    Boolean,
+    EnumRef,
+    Record,
     Integer,
     String,
     TypeRef,
     Optional,
+    UnionRef,
 )
 from hiku.scalar import Scalar
 from hiku.graph import apply
@@ -86,6 +90,15 @@ def serialize(cls, value: Any) -> int:
                 Option('id', Integer),
             ],
         ),
+        Link(
+            'bucket',
+            UnionRef['Bucket'],
+            link_resolver,
+            requires=None,
+            options=[
+                Option('id', Integer),
+            ],
+        ),
     ]),
 ], data_types={
     'Status': Record[{
@@ -153,6 +166,7 @@ def serialize(cls, value: Any) -> int:
 
     extend type Query {
       order(id: Int!): Order
+      bucket(id: Int!): Bucket!
     }
     %s
     scalar Any
@@ -205,5 +219,4 @@ def test_print_introspected_graph_sdl():
     ])
 
     sdl = print_sdl(INTROSPECTED_GRAPH)
-
     assert sdl.strip() == textwrap.dedent(expected).strip()
diff --git a/tests_pg/conftest.py b/tests_pg/conftest.py
index 5e52fef..2728766 100644
--- a/tests_pg/conftest.py
+++ b/tests_pg/conftest.py
@@ -21,7 +21,7 @@ def db_dsn_fixture(request):
     db_dsn = 'postgresql://postgres:postgres@{}:5432/{}'.format(host, name)
 
     pg_engine = sqlalchemy.create_engine(pg_dsn)
-    pg_engine.raw_connection()\
+    pg_engine.raw_connection() \
         .set_isolation_level(psycopg2.extensions.ISOLATION_LEVEL_AUTOCOMMIT)
     pg_engine.execute('CREATE DATABASE {0}'.format(name))
     pg_engine.dispose()