1diff --git a/diffseq.h b/diffseq.h
2index 1974c36..02ef9f2 100644
3--- a/diffseq.h
4+++ b/diffseq.h
5@@ -207,7 +207,7 @@ diag (OFFSET xoff, OFFSET xlim, OFFSET yoff, OFFSET ylim,
6   for (c = 1;; ++c)
7     {
8       OFFSET d;                 /* Active diagonal. */
9-      bool big_snake = false;
10+      bool big_snake _GL_UNUSED = false;
11
12       /* Extend the top-down search by an edit step in each diagonal. */
13       if (fmin > dmin)
14