diff --git a/spacy/tokens/_serialize.py b/spacy/tokens/_serialize.py
index b7bc881c5..25e60f6d8 100644
--- a/spacy/tokens/_serialize.py
+++ b/spacy/tokens/_serialize.py
@@ -6,6 +6,7 @@ import gzip
 import copyreg
 from thinc.neural.ops import NumpyOps
 
+from ..tokens import Doc
 from ..attrs import SPACY, ORTH