diff --git a/simulation/test_tracker.cpp b/simulation/test_tracker.cpp
index 36fa89162..54cdc63e7 100644
--- a/simulation/test_tracker.cpp
+++ b/simulation/test_tracker.cpp
@@ -745,7 +745,7 @@ TORRENT_TEST(tracker_ipv6_argument)
 			TEST_CHECK(pos != std::string::npos);
 			got_ipv6 = pos != std::string::npos;
 			// make sure the IPv6 argument is url encoded
-			TEST_CHECK(req.substr(pos + 6, req.find_first_of(pos + 6, '&'))
+			TEST_CHECK(req.substr(pos + 6, req.find_first_of('&', pos + 6))
 				== "ffff%3a%3a1337");
 			return sim::send_response(200, "OK", 11) + "d5:peers0:e";
 		}