diff --git a/testsuite/lib/generic.sh b/testsuite/lib/generic.sh
index 3645ff52..8cef20fa 100644
--- a/testsuite/lib/generic.sh
+++ b/testsuite/lib/generic.sh
@@ -87,7 +87,11 @@ ts_qdisc_available()
 
 rand_dev()
 {
-    echo "dev-$(head -c 250 /dev/urandom | tr -dc '[:alpha:]' | head -c 6)"
+    rnd=""
+    while [ ${#rnd} -ne 6 ]; do
+        rnd="$(head -c 250 /dev/urandom | tr -dc '[:alpha:]' | head -c 6)"
+    done
+    echo "dev-$rnd"
 }
 
 pr_failed()