diff --git a/bin/tests/system/dlzexternal/driver.c b/bin/tests/system/dlzexternal/driver.c
index 2e59a13e77..310220b1b7 100644
--- a/bin/tests/system/dlzexternal/driver.c
+++ b/bin/tests/system/dlzexternal/driver.c
@@ -166,7 +166,7 @@ del_name(struct dlz_example_data *state, struct record *list,
 
 static isc_result_t
 fmt_address(isc_sockaddr_t *addr, char *buffer, size_t size) {
-	char addr_buf[100];
+	char addr_buf[INET6_ADDRSTRLEN];
 	const char *ret;
 	uint16_t port = 0;