diff --git a/tests/ssl-opt.sh b/tests/ssl-opt.sh
index e08dbec51..724d62791 100755
--- a/tests/ssl-opt.sh
+++ b/tests/ssl-opt.sh
@@ -1233,22 +1233,24 @@ SRV_DELAY_SECONDS=0
 
 # fix commands to use this port, force IPv4 while at it
 # +SRV_PORT will be replaced by either $SRV_PORT or $PXY_PORT later
+# Note: Using 'localhost' rather than 127.0.0.1 here is unwise, as on many
+# machines that will resolve to ::1, and we don't want ipv6 here.
 P_SRV="$P_SRV server_addr=127.0.0.1 server_port=$SRV_PORT"
 P_CLI="$P_CLI server_addr=127.0.0.1 server_port=+SRV_PORT"
 P_PXY="$P_PXY server_addr=127.0.0.1 server_port=$SRV_PORT listen_addr=127.0.0.1 listen_port=$PXY_PORT ${SEED:+"seed=$SEED"}"
 O_SRV="$O_SRV -accept $SRV_PORT"
-O_CLI="$O_CLI -connect localhost:+SRV_PORT"
+O_CLI="$O_CLI -connect 127.0.0.1:+SRV_PORT"
 G_SRV="$G_SRV -p $SRV_PORT"
 G_CLI="$G_CLI -p +SRV_PORT"
 
 if [ -n "${OPENSSL_LEGACY:-}" ]; then
     O_LEGACY_SRV="$O_LEGACY_SRV -accept $SRV_PORT -dhparam data_files/dhparams.pem"
-    O_LEGACY_CLI="$O_LEGACY_CLI -connect localhost:+SRV_PORT"
+    O_LEGACY_CLI="$O_LEGACY_CLI -connect 127.0.0.1:+SRV_PORT"
 fi
 
 if [ -n "${OPENSSL_NEXT:-}" ]; then
     O_NEXT_SRV="$O_NEXT_SRV -accept $SRV_PORT"
-    O_NEXT_CLI="$O_NEXT_CLI -connect localhost:+SRV_PORT"
+    O_NEXT_CLI="$O_NEXT_CLI -connect 127.0.0.1:+SRV_PORT"
 fi
 
 if [ -n "${GNUTLS_NEXT_SERV:-}" ]; then