diff --git a/testssl.sh b/testssl.sh
index ac90014..65909eb 100755
--- a/testssl.sh
+++ b/testssl.sh
@@ -19340,7 +19340,15 @@ parse_cmd_line() {
           fatal "URI missing" $ERR_CMDLINE
      else
      # left off here is the URI
-          URI="$1"
+          if [[ $1 = *[![:ascii:]]* ]]; then
+              if [[ "$(command -v idn)" == "" ]]; then
+                  fatal "URI contains non-ASCII characters, and IDN not available."
+              else
+                  URI="$(echo $1 | idn)"
+              fi
+          else
+              URI="$1"
+          fi
           # parameter after URI supplied:
           [[ -n "$2" ]] && fatal "URI comes last" $ERR_CMDLINE
      fi