diff --git a/spacy/vectors.pyx b/spacy/vectors.pyx
index 6c5018d13..1e4e97c38 100644
--- a/spacy/vectors.pyx
+++ b/spacy/vectors.pyx
@@ -85,7 +85,7 @@ cdef class Vectors:
         return len(self.key2row)
 
     def __reduce__(self):
-        keys_and_rows = self.key2row.items()
+        keys_and_rows = tuple(self.key2row.items())
         return (unpickle_vectors, (keys_and_rows, self.data))
 
     def __getitem__(self, key):