diff --git a/re.c b/re.c
index d7766905bb..63cfc026de 100644
--- a/re.c
+++ b/re.c
@@ -3519,7 +3519,7 @@ rb_reg_quote(VALUE str)
     t = RSTRING_PTR(tmp);
     /* copy upto metacharacter */
     const char *p;
-    long n;
+    long MAYBE_UNUSED(n);
     RSTRING_GETMEM(str, p, n);
     memcpy(t, p, s - p);
     t += s - p;