diff --git a/spacy/tokens/_retokenize.pyx b/spacy/tokens/_retokenize.pyx
index 55ad909bb..741be7e6a 100644
--- a/spacy/tokens/_retokenize.pyx
+++ b/spacy/tokens/_retokenize.pyx
@@ -146,6 +146,7 @@ def _merge(Doc doc, merges):
         syntactic root of the span.
     RETURNS (Token): The first newly merged token.
     """
+    cdef int i, merge_index, start, end, token_index
     cdef Span span
     cdef const LexemeC* lex
     cdef TokenC* token