diff --git a/spacy/syntax/transition_system.pyx b/spacy/syntax/transition_system.pyx
index 9e624bd58..a4bb02753 100644
--- a/spacy/syntax/transition_system.pyx
+++ b/spacy/syntax/transition_system.pyx
@@ -1,3 +1,4 @@
+# cython: infer_types=True
 from cymem.cymem cimport Pool
 from thinc.typedefs cimport weight_t
 from collections import defaultdict