diff --git a/res/scripts/stdlib.lua b/res/scripts/stdlib.lua
index a5f69883..66f1885f 100644
--- a/res/scripts/stdlib.lua
+++ b/res/scripts/stdlib.lua
@@ -136,3 +136,7 @@ function toml.parse(s)
     end
     return output
 end
+
+function pack.is_installed(packid)
+    return file.isfile(packid..":package.json")
+end