diff --git a/bin/tests/system/rndc/gencheck.c b/bin/tests/system/rndc/gencheck.c
index d72078782a..df03aaa0f8 100644
--- a/bin/tests/system/rndc/gencheck.c
+++ b/bin/tests/system/rndc/gencheck.c
@@ -79,7 +79,7 @@ main(int argc, char **argv)
 	ret = EXIT_SUCCESS;
 
  out:
-	printf("%zu\n", length);
+	printf("%lu\n", (unsigned long)length);
 
 	if (fd != -1)
 		close(fd);