diff --git a/run-with-xdummy.sh b/run-with-xdummy.sh
index 619a164..c73b03f 100755
--- a/run-with-xdummy.sh
+++ b/run-with-xdummy.sh
@@ -46,7 +46,7 @@ printf -- '%s\n' "Creating \"${CONTAINER_NAME:?}\" container..."
 	--publish 3322:3322/tcp \
 	--publish 3389:3389/tcp \
 	--env ENABLE_XDUMMY=true \
-	${CONTAINER_DEVICES} \
+	${CONTAINER_DEVICES?} \
 	"${IMAGE_NAME:?}" "$@" >/dev/null
 
 printf -- '%s\n\n' 'Done!'
diff --git a/run.sh b/run.sh
index 3493ddd..682184c 100755
--- a/run.sh
+++ b/run.sh
@@ -45,7 +45,7 @@ printf -- '%s\n' "Creating \"${CONTAINER_NAME:?}\" container..."
 	--shm-size 2g \
 	--publish 3322:3322/tcp \
 	--publish 3389:3389/tcp \
-	${CONTAINER_DEVICES} \
+	${CONTAINER_DEVICES?} \
 	"${IMAGE_NAME:?}" "$@" >/dev/null
 
 printf -- '%s\n\n' 'Done!'