diff --git a/spacy/vocab.pxd b/spacy/vocab.pxd
index 89e22ed25..dabceb38a 100644
--- a/spacy/vocab.pxd
+++ b/spacy/vocab.pxd
@@ -20,12 +20,6 @@ cdef struct _Cached:
     int length
 
 
-cdef inline void slice_unicode(UniStr* s, Py_UNICODE* chars, int start, int end) nogil:
-    s.chars = &chars[start]
-    s.n = end - start
-    s.key = hash64(s.chars, s.n * sizeof(Py_UNICODE), 0)
-
-
 cdef class Vocab:
     cpdef public get_lex_props
     cdef Pool mem
diff --git a/spacy/vocab.pyx b/spacy/vocab.pyx
index 6c19d277e..80f702572 100644
--- a/spacy/vocab.pyx
+++ b/spacy/vocab.pyx
@@ -4,6 +4,7 @@ from os import path
 
 from .lexeme cimport EMPTY_LEXEME
 from .lexeme cimport init as lexeme_init
+from .strings cimport slice_unicode
 
 
 cdef class Vocab: