How do I install Quark Zeta Fixin?

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. Opens on CurseForge — not every file is mirrored on our own servers.

What Minecraft version does Quark Zeta Fixin work with?

The listing gives Minecraft 1.20.1, 1.21.1. This is the version stated by the author or source site, not something we verified ourselves.

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Quark Zeta Fixin

Java mod listed for Minecraft 1.20–1.21. Downloads from the MC Java Mods app on Android.

by ChiefArug · on CurseForge

Which build do you need?

This mod ships a separate file for every mod loader and every version of the game. Pick both, then download — the wrong build installs fine and then does nothing in the game.

Mod loader

Mod loader Forge1 build
Mod loader NeoForge1 build

Minecraft version

Minecraft 1.20.1–1.21.1Newest

Minecraft 1.20.1–1.21.1Newest

⬇ Download for 1.20.1–1.21.1 · Forge ⬇ Download for 1.20.1–1.21.1 · NeoForge

I don't know my version or loader

Open the Minecraft launcher and look at the profile you play on — it names both, like fabric-loader-1.21.4. The version also shows in the bottom-right corner of the game's main menu.

No loader in the profile name? Then it's plain Minecraft, and these mods won't run — you need Fabric or NeoForge installed first.

Open in MC Java Mods Get it on Google Play →

This mod fixes concurrency issues with Zeta (the library for Quark)'s event system, where having any number of addons that try use it (although more commonly with lots of addons) will cause the game to crash sometimes.

Error messages that this fix look like this:

	Exception message: java.lang.ArrayIndexOutOfBoundsException: Index 512 out of bounds for length 257
Stacktrace:
	at it.unimi.dsi.fastutil.objects.Object2ObjectOpenHashMap.rehash(Object2ObjectOpenHashMap.java:1275)
	at it.unimi.dsi.fastutil.objects.Object2ObjectOpenHashMap.insert(Object2ObjectOpenHashMap.java:245)
	at it.unimi.dsi.fastutil.objects.Object2ObjectOpenHashMap.put(Object2ObjectOpenHashMap.java:253)
	at org.violetmoon.zetaimplforge.event.ForgeZetaEventBus.subscribeMethod(ForgeZetaEventBus.java:87)

The important parts here are the Exception message: java.lang.ArrayIndexOutOfBoundsException: AND the org.violetmoon.zetaimplforge.event.ForgeZetaEventBus.subscribeMethod. If both of these do not appear in your error message then this will not solve your issue.

It fixes this by replacing the non thread safe map with a thread safe version, and does so in a way that means the game will not crash no matter what changes Zeta makes (even if they fix this issue). You should still remove this mod when Zeta fixes the issue though.

And yes, this mod is so small that the same jar works across 1.20.1 Forge and 1.21.1 NeoForge.

Quick facts

Edition: Minecraft Java
File type: .jar
Minecraft versions listed: 1.20.1, 1.21.1
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 CurseForge — 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.

File checked by MCModsHub

Ships as quarkzetafixin-1.0.jar — drop this file into the mods folder
Download size: 104 KB
Download link checked 3 Oct 2026 — working

These come from our own check of the pack file, not from the source page.

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All Mods for Java All Minecraft Java mods Java mods for 1.20 Java mods for 1.21