diff --git a/package/base-files/files/sbin/sysupgrade b/package/base-files/files/sbin/sysupgrade
index 88e154e39e..c27857a022 100755
--- a/package/base-files/files/sbin/sysupgrade
+++ b/package/base-files/files/sbin/sysupgrade
@@ -395,7 +395,7 @@ json_get_var forceable "forceable"
 }
 
 if [ -n "$CONF_IMAGE" ]; then
-	case "$(get_magic_word $CONF_IMAGE cat)" in
+	case "$(get_magic_word "$CONF_IMAGE" cat)" in
 		# .gz files
 		1f8b) ;;
 		*)