Registry / world corruption (unregistered block or entity)
Registry corruption happens when a Minecraft world contains blocks, items, biomes, or entities from a mod that's no longer in mods/. The world was saved with the assumption those IDs would exist; on load Minecraft hits the missing reference and refuses to continue. The fix is either restoring the missing mod, or stripping the unknown references from the world.
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How to fix it
- 1
Identify the missing registry entry
The crash names the missing ID, e.g. 'create:rotation_speed_controller' or 'twilightforest:naga_courtyard_main'. The part before the colon is the mod ID. That's the mod that's no longer loaded.
- 2
Restore the missing mod from a backup
The cleanest fix: put the mod's .jar back in mods/ and the world loads normally. If the pack auto-updated and the mod was renamed/replaced, find the same project on CurseForge / Modrinth — sometimes a new project ID points to the same content.
- 3
If the mod is genuinely gone, restore the world from before the removal
If you can't get the mod back (it was deleted, the modpack version changed structurally), the cleanest fix is restoring a world backup from before the mod was removed. Players lose recent progress, but the world boots clean.
- 4
Last resort — strip unknown entries with a tool
Tools like Universal Mod Core (UMC) for Forge can scan a world and remove block/entity references to unloaded mods. The blocks become air, entities disappear. Use this only when other options are gone — it permanently alters the world. Back up first.
Alternative causes
These can produce the same error message — worth ruling out if the steps above don't resolve it.
Mod present but registry name changed between versions
Some mods rename internal IDs across versions (rare but it happens). The mod is in mods/ but the world still references the old name. Check the mod's changelog for breaking ID changes and apply the migration the author suggests.
Datapack referencing a missing biome or feature
Custom datapacks add registry entries too. If a datapack was removed but the world still references its biomes or features, you get the same error. Either restore the datapack (in world/datapacks/) or strip the references.
Frequently asked
Will the world be corrupt forever if I lose a mod?
Not necessarily. Most worlds survive a missing mod with tool-assisted stripping. The lost content (blocks placed, mobs in chunks) is gone, but the structural data (terrain, player inventories, base layout) usually survives.
Why does removing a mod work fine on some worlds but not others?
Depends on whether the world ACTUALLY USED the mod's content. A mod added to mods/ but never producing blocks/entities is safe to remove. One whose blocks are placed in the world is not.
What's the difference between a missing block and a missing biome?
Missing block: a specific position has an unknown ID; usually a hard crash. Missing biome: a chunk's biome is unknown; sometimes recoverable (the biome falls back to plains), sometimes a crash. Biome mods are riskier to remove than block mods.
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Last reviewed 2026-06-05. If a step is wrong or out of date, tell us — we'll fix the article and the auto-pattern at the same time.