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Troubleshooting: Java 17 (64-Bit) for Minecraft 1.18 – 1.20.4

1 minHow-to
How-tofix java 17 temurin minecraft 1 18 1 20 4 errorprism launcher java crash minecraft 1.18, 1.19, 1.20.1 – 1.20.4unsupportedclassversionerror prism launcher

Step-by-step fix for Java version mismatches and JVM launch errors on Minecraft 1.18, 1.19, 1.20.1 – 1.20.4.

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Target Runtime
Java 17 (64-Bit) for Minecraft 1.18 – 1.20.4
Minecraft Target
Minecraft 1.18, 1.19, 1.20.1 – 1.20.4
Vendor
Eclipse Adoptium Temurin 17 LTS

Diagnosing Java 17 (64-Bit) for Minecraft 1.18 – 1.20.4 startup failures

If your instance on **Minecraft 1.18, 1.19, 1.20.1 – 1.20.4** exits immediately after clicking Launch, open the **Minecraft Log** tab. An `UnsupportedClassVersionError` or `Incompatible magic value` means the instance is overriding the global runtime with the wrong Java version.

Follow our Java 17 (64-Bit) for Minecraft 1.18 – 1.20.4 reference to point the instance at a verified 64-bit `javaw.exe`.

Prism Launcher screenshot showing the instance management user-interface
Each instance has its own version, mods, settings and worlds.

3-step repair in Prism Launcher

  1. Right-click the failing instance → **Edit** → **Settings** → **Java**.
  2. Tick **Java installation**, click **Auto-detect** (or download via Prism), and choose **Eclipse Adoptium Temurin 17 LTS**.
  3. Click **Test** to confirm the runtime starts cleanly, then launch your world. Need a fresh launcher install? Visit /download.

Frequently asked questions

What if clicking Test says 'Could not reserve enough space for object heap'?

You either selected a 32-bit Java installation or set Maximum Memory higher than the free physical RAM currently available on Windows.

Should I check 'Skip Java compatibility checks'?

Only enable that toggle for special backported modpacks (such as GTNH Java 17/21 builds on 1.7.10); for normal packs, switch to the matching Java version instead.

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Prism Launcher on Windows showing several modpacks and instances