diff --git a/tools/testing/selftests/net/mptcp/simult_flows.sh b/tools/testing/selftests/net/mptcp/simult_flows.sh
index 7b9aabe10170..d723261bdc62 100755
--- a/tools/testing/selftests/net/mptcp/simult_flows.sh
+++ b/tools/testing/selftests/net/mptcp/simult_flows.sh
@@ -24,6 +24,7 @@ small=""
 sout=""
 cout=""
 capout=""
+capprefix=""
 size=0
 
 usage() {
@@ -70,6 +71,11 @@ setup()
 
 	mptcp_lib_ns_init ns1 ns2 ns3
 
+	if $capture; then
+		capprefix="simult_flows-${ns1:4}"
+		mptcp_lib_pr_info "pcap will have this prefix: ${capprefix}-"
+	fi
+
 	ip link add ns1eth1 netns "$ns1" type veth peer name ns2eth1 netns "$ns2"
 	ip link add ns1eth2 netns "$ns1" type veth peer name ns2eth2 netns "$ns2"
 	ip link add ns2eth3 netns "$ns2" type veth peer name ns3eth1 netns "$ns3"
@@ -136,14 +142,13 @@ do_transfer()
 
 	if $capture; then
 		local capuser
-		local rndh="${ns1:4}"
 		if [ -z $SUDO_USER ] ; then
 			capuser=""
 		else
 			capuser="-Z $SUDO_USER"
 		fi
 
-		local capfile="${rndh}-${port}"
+		local capfile="${capprefix}-${port}"
 		local capopt="-i any -s 65535 -B 32768 ${capuser}"
 
 		ip netns exec ${ns3}  tcpdump ${capopt} -w "${capfile}-listener.pcap"  >> "${capout}" 2>&1 &