diff --git a/ztest.c b/ztest.c
index 2663c90..3947670 100644
--- a/ztest.c
+++ b/ztest.c
@@ -294,7 +294,7 @@ average_time (const size_t *times, size_t trials)
 /* Test a larger text, if available.  */
 
 static void
-test_large (struct backtrace_state *state)
+test_large (struct backtrace_state *state ATTRIBUTE_UNUSED)
 {
 #ifdef HAVE_ZLIB
   unsigned char *orig_buf;