diff --git a/start-captive-wmaker.sh b/start-captive-wmaker.sh
index 32a5f402..2afb4c33 100755
--- a/start-captive-wmaker.sh
+++ b/start-captive-wmaker.sh
@@ -77,10 +77,18 @@ if [ -n "$1" -a -x "$WindowMaker$1" ] ; then
     shift
 fi
 
-Xephyr -screen 1080x760 :1 &
+for i in $(seq 5 10) ; do
+    if [ "x$DISPLAY" != "x:$i" ] ; then
+        xephyr_display=":$i"
+        break
+    fi
+done
+echo "Running Xephyr on display $xephyr_display"
+
+Xephyr -screen 640x480 "$xephyr_display" &
 xephyr_pid=$!
-DISPLAY=:1 gdb \
+DISPLAY="$xephyr_display" gdb \
            --directory "$project_base" \
            --quiet \
-           --args "$WindowMaker" -display :1 --for-real "$@"
+           --args "$WindowMaker" -display "$xephyr_display" --for-real "$@"
 kill $xephyr_pid