diff --git a/test/unit/etharp/test_etharp.c b/test/unit/etharp/test_etharp.c
index 96a32420..8eb506c1 100644
--- a/test/unit/etharp/test_etharp.c
+++ b/test/unit/etharp/test_etharp.c
@@ -139,7 +139,7 @@ START_TEST(test_etharp_table)
 #if ETHARP_SUPPORT_STATIC_ENTRIES
   err_t err;
 #endif /* ETHARP_SUPPORT_STATIC_ENTRIES */
-  s8_t idx;
+  ssize_t idx;
   const ip4_addr_t *unused_ipaddr;
   struct eth_addr *unused_ethaddr;
   struct udp_pcb* pcb;