diff --git a/src/define.sh b/src/define.sh
index 24d5f79..5bc3223 100644
--- a/src/define.sh
+++ b/src/define.sh
@@ -1,6 +1,8 @@
 #!/usr/bin/env bash
 set -Eeuo pipefail
 
+: "${XRES:=""}"
+: "${YRES:=""}"
 : "${VERIFY:=""}"
 : "${REGION:=""}"
 : "${MANUAL:=""}"