diff --git a/test/mock_relay.cpp b/test/mock_relay.cpp
index e0f3dae..166838d 100644
--- a/test/mock_relay.cpp
+++ b/test/mock_relay.cpp
@@ -1232,6 +1232,12 @@ TEST(relay, outbond_callback) {
   EXPECT_GLOBAL_CALL(recvfrom, recvfrom(_, _, _, _, _, _)).Times(5).WillOnce(Return(0))
     .WillOnce(Return(2)).WillOnce(Return(0))
     .WillOnce(Return(msg_len)).WillOnce(Return(0));
+
+  char ethernet1[IF_NAMESIZE] = "Ethernet1";
+  char ptr[20] = "vlan";
+  EXPECT_GLOBAL_CALL(if_indextoname, if_indextoname(_, _)).Times(2).WillOnce(Return(nullptr))
+                    .WillOnce(DoAll(SetArrayArgument<1>(ethernet1, ethernet1 + IF_NAMESIZE), Return(ptr)));
+
   ASSERT_NO_THROW(outbond_callback(0, 0, state_db.get()));
   // cover 0 < buffer_sz < sizeof(struct dhcpv6_msg)
   ASSERT_NO_THROW(outbond_callback(0, 0, state_db.get()));