
Summary
This mod fixes the Class Loader in legacy versions of Minecraft.
Details
This is a simple jar-mod which adds the CodeSource to each loaded class in FML.
That is actually everything this mod does (well, besides fixing a few more bugs on even older versions of Forge).
This mod just ships a backported RelaunchClassLoader which overwrites the built-in version (from FML) and allows mods to read the file source of classes.
Why is this needed in some cases?
For example, Block Helper is able to show you in the item tooltips which mod a given item is from.
This procedure relies on the CodeSource object of the ProtectionDomains of the loaded classes.
Old versions of FML do not set this CodeSource, which leads Block Helper into thinking that everything is a Vanilla item.
Installation
As a ModLoaderMP / Forge mod
This mod needs to be installed as a jar-mod. That means, you have to...
- Be sure to back up your
minecraft.jar! - Extract the content of the mod zip into the
minecraft.jarfile - Delete the
META-INFfolder in there - Overwrite any existing files when doing so!
- ???
- Profit!
As a Fabric mod
I do not have any Fabric versions available. However, the fix is incorporated directly into Fabricated Legacy Forge. Hence, you do not need to install it separately!
Unsupported mods
- ObsidiPlates 1.4.2 was incompatible with v1. This is fixed in v2.
Please let me know about any incompatibilities! :)
- Edition: Minecraft Java
- File type: .jar
- Minecraft versions listed: 1.3.1, 1.3.2, 1.4
- How to install: Install the matching mod loader (Forge, Fabric or NeoForge) for your Minecraft version. → Download the .jar. → Put it in the .minecraft/mods folder and launch that loader profile.
- Where to get it: Opens on Modrinth — not every file is mirrored on our own servers.
Install steps are the general flow for this file type — How to install Minecraft Java mods & modpacks walks through it step by step.
- Downloads as ClassLoaderFixer-2.zip
- Download size: 6 KB
- Download link checked 31 Aug 2026 — working
These come from our own check of the pack file, not from the source page.