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Minecraft

Minecraft Java 17 UnsupportedClassVersionError Fix

If your Minecraft crash log says UnsupportedClassVersionError, your modpack is probably running with the wrong Java version. This is common when a newer Minecraft version needs Java 17, but the launcher is still using Java 8.

Quick answer

Install Java 17 and set your Minecraft launcher, CurseForge, Prism Launcher, Modrinth, or custom profile to use Java 17. Then relaunch the game and load a fresh crash log if the issue continues.

What this error means

UnsupportedClassVersionError means Java tried to load a file that was built for a newer Java version than the one currently running. The mod itself may be fine — the launcher may just be pointing at an older Java install.

Common signs in the crash log

java.lang.UnsupportedClassVersionError
Unsupported class file major version
has been compiled by a more recent version of the Java Runtime
class file version 61.0
Java 8 is being used with a Java 17 modpack
The launcher is pointing to the wrong Java path

How to fix it

1
Check the Minecraft version your modpack uses.
2
For many Minecraft 1.18+ modpacks, install or select Java 17.
3
Open your launcher settings for that profile or instance.
4
Find the Java executable or Java version setting.
5
Point the launcher to Java 17 instead of Java 8.
6
Save the profile, relaunch Minecraft, and test again.
7
If it still crashes, load the newest log created after that relaunch.

Which Java version do I need?

Minecraft 1.16.5 and older modpacks often use Java 8.
Minecraft 1.17 commonly uses Java 16.
Minecraft 1.18, 1.19, and 1.20 modpacks usually use Java 17.
Some newer setups may require a newer Java version, so always check the modpack notes.

Do not do this yet

Do not delete random mods before checking the Java version.
Do not reinstall the entire modpack first if the log clearly says UnsupportedClassVersionError.
Do not assume the newest Java always fixes every Minecraft version.
Do not change every launcher setting at once. Change Java first, then retest.

FixMyGame tip

If FixMyGame says Java mismatch but you already installed Java 17, check the launcher profile. Installing Java 17 is not enough if the launcher is still using an older Java path.

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