diff --git a/tools/testing/selftests/net/mptcp/mptcp_join.sh b/tools/testing/selftests/net/mptcp/mptcp_join.sh
index 34152a50a3e2..8023c0773d95 100755
--- a/tools/testing/selftests/net/mptcp/mptcp_join.sh
+++ b/tools/testing/selftests/net/mptcp/mptcp_join.sh
@@ -1054,13 +1054,38 @@ chk_fail_nr()
 {
 	local fail_tx=$1
 	local fail_rx=$2
+	local ns_invert=${3:-""}
 	local count
 	local dump_stats
+	local ns_tx=$ns1
+	local ns_rx=$ns2
+	local extra_msg=""
+	local allow_tx_lost=0
+	local allow_rx_lost=0
+
+	if [[ $ns_invert = "invert" ]]; then
+		ns_tx=$ns2
+		ns_rx=$ns1
+		extra_msg=" invert"
+	fi
+
+	if [[ "${fail_tx}" = "-"* ]]; then
+		allow_tx_lost=1
+		fail_tx=${fail_tx:1}
+	fi
+	if [[ "${fail_rx}" = "-"* ]]; then
+		allow_rx_lost=1
+		fail_rx=${fail_rx:1}
+	fi
 
 	printf "%-${nr_blank}s %s" " " "ftx"
-	count=$(ip netns exec $ns1 nstat -as | grep MPTcpExtMPFailTx | awk '{print $2}')
+	count=$(ip netns exec $ns_tx nstat -as | grep MPTcpExtMPFailTx | awk '{print $2}')
 	[ -z "$count" ] && count=0
 	if [ "$count" != "$fail_tx" ]; then
+		extra_msg="$extra_msg,tx=$count"
+	fi
+	if { [ "$count" != "$fail_tx" ] && [ $allow_tx_lost -eq 0 ]; } ||
+	   { [ "$count" -gt "$fail_tx" ] && [ $allow_tx_lost -eq 1 ]; }; then
 		echo "[fail] got $count MP_FAIL[s] TX expected $fail_tx"
 		fail_test
 		dump_stats=1
@@ -1069,17 +1094,23 @@ chk_fail_nr()
 	fi
 
 	echo -n " - failrx"
-	count=$(ip netns exec $ns2 nstat -as | grep MPTcpExtMPFailRx | awk '{print $2}')
+	count=$(ip netns exec $ns_rx nstat -as | grep MPTcpExtMPFailRx | awk '{print $2}')
 	[ -z "$count" ] && count=0
 	if [ "$count" != "$fail_rx" ]; then
+		extra_msg="$extra_msg,rx=$count"
+	fi
+	if { [ "$count" != "$fail_rx" ] && [ $allow_rx_lost -eq 0 ]; } ||
+	   { [ "$count" -gt "$fail_rx" ] && [ $allow_rx_lost -eq 1 ]; }; then
 		echo "[fail] got $count MP_FAIL[s] RX expected $fail_rx"
 		fail_test
 		dump_stats=1
 	else
-		echo "[ ok ]"
+		echo -n "[ ok ]"
 	fi
 
 	[ "${dump_stats}" = 1 ] && dump_stats
+
+	echo "$extra_msg"
 }
 
 chk_fclose_nr()
@@ -2654,6 +2685,7 @@ fail_tests()
 	if reset_with_fail "Infinite map" 1; then
 		run_tests $ns1 $ns2 10.0.1.1 128
 		chk_join_nr 0 0 0 +1 +0 1 0 1 "$(pedit_action_pkts)"
+		chk_fail_nr 1 -1 invert
 	fi
 }