Memory Leak Fix 1.1.5 for Minecraft 1.17–1.20.4: When You Need It

Memory Leak Fix is a targeted repair mod for older Minecraft Java versions. It fixes several memory leaks on the client and server. Its useful audience is players keeping an older world or modpack running—not everyone installing a new version of Minecraft.

On Minecraft 1.20.5 and newer, the author says the vanilla leaks addressed by this mod have already been fixed. Do not add an old Memory Leak Fix JAR to a modern pack simply because an optimisation checklist mentions it.

Do you need this mod?

What does a memory leak look like in play?

Think of leaving one world and opening another during the same Minecraft session. On affected older versions, a reference left behind by the client could keep the previous world in memory after returning to the menu. The mod fixes that specific retention problem; you do not activate it with a key or an item.

Other historical fixes involve cached biome temperatures, entity memories and allocations left behind when texture loading or a large screenshot fails. Which fixes matter depends on your Minecraft version: several were already repaired by Mojang before the mod became entirely obsolete.

A climbing memory reading alone is not proof of a leak. Loading chunks and textures also uses memory. The useful question is whether the same repeated activity causes persistent trouble, rather than whether a single number briefly rises.

Download Memory Leak Fix 1.1.5

Choose one file for Minecraft Java 1.17–1.20.4. Fabric/Quilt and Forge use different builds; do not install both.

Fabric and Quilt

Memory Leak Fix 1.1.5 — Fabric and Quilt, Minecraft 1.17–1.20.4 48.18 Kb1 downloads View download

For Fabric, this release requires Fabric Loader 0.15.0 or newer. Update the loader for the same Minecraft instance if the game reports an outdated loader.

Forge

Memory Leak Fix 1.1.5 — Forge, Minecraft 1.17–1.20.4 222.58 Kb1 downloads View download

Use Forge for your exact Minecraft version. These are not NeoForge downloads.

Playing an older version?

The same mod version number does not mean the files are interchangeable. The release list separates newer and older Minecraft ranges, then separates loaders.

The two downloads above are the 1.17–1.20.4 builds. For the older ranges, use the creator’s separate older release listed on the official project page. Keep Fabric and Forge files separate when maintaining more than one Minecraft instance.

Install it in the Minecraft instance you use

1. Confirm the instance’s Minecraft version and mod loader.
2. Download its matching Memory Leak Fix JAR.
3. Place that file in the instance’s mods folder. Do not keep multiple versions of the same mod there.
4. Launch the instance and check that the loader accepts the mod without a compatibility error.

The project supports both client and server environments. A client installation addresses the client; it does not silently install a repair on a server you join. Server operators must use a matching server-side installation when relevant.

What improvement should you expect?

A leak fix helps with the specific memory-retention problems it addresses. It is not a command to allocate more memory, a texture-quality setting or a promise of a particular FPS increase. A brief screenshot of a lower memory reading is not enough to prove that a long-session problem has disappeared.

If you are comparing behaviour, use the same Minecraft instance and repeat the session that caused the problem. Keep the other mods and graphics settings unchanged while comparing. If the issue remains, a different mod or workload may be responsible.

Can you use it with other optimisation mods?

The author recommends Lithium and FerriteCore alongside it for their different optimisation roles. That recommendation does not mean you should install every performance mod you find, or use a build for the wrong loader. Match each one to the Minecraft instance.

What if a modern version still uses too much memory?

The author’s 1.20.5 cutoff applies to the leaks this project fixes, not every possible memory problem in Minecraft or third-party mods. Note when the problem appears—after joining worlds, using a particular mod, or playing for a long time—and investigate that situation. An obsolete repair cannot be assumed to solve a new cause.

Keep an older pack useful without adding unnecessary mods

For an established 1.20.1 pack, check its mod list before installing another copy. If it already includes the correct Memory Leak Fix build, there is no second activation step. For a newer pack, leave this legacy repair out and use the troubleshooting information for the actual mod or activity causing trouble.

Removing this background repair does not remove new blocks or items from your world, because adding content is not its purpose. Close Minecraft before changing the mod folder and keep the pack’s documented dependencies together.