diff --git a/tests/ssl-opt.sh b/tests/ssl-opt.sh
index 23f19ea27..6813754bc 100755
--- a/tests/ssl-opt.sh
+++ b/tests/ssl-opt.sh
@@ -372,7 +372,7 @@ fi
 
 # Pick a "unique" port in the range 10000-19999.
 PORT="0000$$"
-PORT="1$(echo $PORT | tail -c 5)"
+PORT="1$( printf $PORT | tail -c 4 )"
 
 # fix commands to use this port
 P_SRV="$P_SRV server_port=$PORT"