diff --git a/adapters/fabric/src/main/java/art/arcane/iris/fabric/IrisFabricBootstrap.java b/adapters/fabric/src/main/java/art/arcane/iris/fabric/IrisFabricBootstrap.java
index ed8a29270..2357ced88 100644
--- a/adapters/fabric/src/main/java/art/arcane/iris/fabric/IrisFabricBootstrap.java
+++ b/adapters/fabric/src/main/java/art/arcane/iris/fabric/IrisFabricBootstrap.java
@@ -17,6 +17,7 @@ public final class IrisFabricBootstrap implements ModInitializer {
     public void onInitialize() {
         NativeFabricLoader loader = new NativeFabricLoader(new NativeLoaderOptions(
                 "irisworldgen", "treefeller", ModdedTreeFellerService::runBreakProbe));
+        loader.captureOriginalBiomes();
         NativeChunkGeneratorDefinition generator = IrisModdedChunkGenerator.DEFINITION;
         NativeFabricPackSources.bind(ModdedForcedDatapack::repositorySource);
         ModdedEngineBootstrap.bootCommon(loader, "Fabric", () -> NativeFabricBootstrap.registerGenerator(generator));
diff --git a/adapters/fabric/src/test/java/art/arcane/volmlib/nativelib/minecraft26_2/fabric/NativeFabricBiomeDefinitionTest.java b/adapters/fabric/src/test/java/art/arcane/volmlib/nativelib/minecraft26_2/fabric/NativeFabricBiomeDefinitionTest.java
new file mode 100644
index 000000000..85fd92a73
--- /dev/null
+++ b/adapters/fabric/src/test/java/art/arcane/volmlib/nativelib/minecraft26_2/fabric/NativeFabricBiomeDefinitionTest.java
@@ -0,0 +1,108 @@
+package art.arcane.volmlib.nativelib.minecraft26_2.fabric;
+
+import art.arcane.volmlib.nativelib.minecraft26_2.terrain.NativeRegistryDefinitions;
+import art.arcane.volmlib.nativelib.modded.NativeLoaderOptions;
+import com.google.gson.JsonParser;
+import com.mojang.serialization.JsonOps;
+import com.mojang.serialization.Lifecycle;
+import net.minecraft.SharedConstants;
+import net.minecraft.core.Holder;
+import net.minecraft.core.HolderSet;
+import net.minecraft.core.MappedRegistry;
+import net.minecraft.core.RegistrationInfo;
+import net.minecraft.core.RegistryAccess;
+import net.minecraft.core.registries.Registries;
+import net.minecraft.resources.Identifier;
+import net.minecraft.resources.RegistryOps;
+import net.minecraft.resources.ResourceKey;
+import net.minecraft.server.Bootstrap;
+import net.minecraft.world.level.biome.Biome;
+import net.minecraft.world.level.biome.BiomeGenerationSettings;
+import net.minecraft.world.level.levelgen.GenerationStep;
+import net.minecraft.world.level.levelgen.carver.WorldCarver;
+import net.minecraft.world.level.levelgen.feature.Feature;
+import net.minecraft.world.level.levelgen.placement.PlacedFeature;
+import org.junit.BeforeClass;
+import org.junit.Test;
+
+import java.lang.reflect.Constructor;
+import java.lang.reflect.Field;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.function.BooleanSupplier;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertTrue;
+import static org.mockito.Mockito.mock;
+
+public class NativeFabricBiomeDefinitionTest {
+    private static final String BIOME_REGISTRY = "minecraft:worldgen/biome";
+    private static final String BIOME_KEY = "iris:biomes/fabric_modified";
+    private static final String SOURCE_JSON = "{\"has_precipitation\":true,\"temperature\":0.8,\"downfall\":0.4,"
+            + "\"effects\":{\"water_color\":\"#3f76e4\"},\"carvers\":[],\"features\":[]}";
+
+    @BeforeClass
+    public static void bootstrap() {
+        SharedConstants.tryDetectVersion();
+        Bootstrap.bootStrap();
+    }
+
+    @Test
+    public void generatedBiomeDefinitionExcludesFabricBiomeModifications() throws Exception {
+        MappedRegistry<PlacedFeature> features = new MappedRegistry<>(Registries.PLACED_FEATURE, Lifecycle.stable());
+        Holder.Reference<PlacedFeature> ore = features.register(
+                ResourceKey.create(Registries.PLACED_FEATURE, Identifier.parse("iris:modded_ore")),
+                new PlacedFeature(Holder.direct(mock(Feature.class)), List.of()),
+                RegistrationInfo.BUILT_IN);
+        features.freeze();
+        MappedRegistry<WorldCarver> carvers = new MappedRegistry<>(Registries.CARVER, Lifecycle.stable());
+        carvers.freeze();
+        MappedRegistry<Biome> biomes = new MappedRegistry<>(Registries.BIOME, Lifecycle.stable());
+        RegistryAccess access = new RegistryAccess.ImmutableRegistryAccess(List.of(biomes, features, carvers));
+        Biome source = Biome.DIRECT_CODEC.parse(RegistryOps.create(JsonOps.INSTANCE, access),
+                JsonParser.parseString(SOURCE_JSON)).getOrThrow();
+        NativeFabricLoader loader = new NativeFabricLoader(new NativeLoaderOptions("irisworldgen", "treefeller",
+                BooleanSupplier::getAsBoolean));
+        loader.recordOriginalBiome(source);
+        Holder.Reference<Biome> biome = biomes.register(
+                ResourceKey.create(Registries.BIOME, Identifier.parse(BIOME_KEY)), source, RegistrationInfo.BUILT_IN);
+        biomes.freeze();
+        addFeatureInPlace(biome.value().getGenerationSettings(), ore);
+        warmInPlace(biome.value());
+        NativeRegistryDefinitions definitions = new NativeRegistryDefinitions(() -> access, loader::unmodifiedBiome);
+
+        assertEquals(0.1F, biome.value().getBaseTemperature(), 0.0F);
+        assertTrue(biome.value().getGenerationSettings().features()
+                .get(GenerationStep.Decoration.UNDERGROUND_ORES.ordinal()).contains(ore));
+        assertEquals(JsonParser.parseString(definitions.canonicalDefinition(BIOME_REGISTRY, BIOME_KEY, SOURCE_JSON).value()),
+                JsonParser.parseString(definitions.generatedDefinition(BIOME_REGISTRY, BIOME_KEY).value()));
+    }
+
+    /**
+     * What a Fabric biome modification that adds an ore does: it replaces the feature list of the registered biome's
+     * own generation settings.
+     */
+    private static void addFeatureInPlace(BiomeGenerationSettings settings, Holder<PlacedFeature> feature)
+            throws ReflectiveOperationException {
+        List<HolderSet<PlacedFeature>> steps = new ArrayList<>(settings.features());
+        while (steps.size() <= GenerationStep.Decoration.UNDERGROUND_ORES.ordinal()) {
+            steps.add(HolderSet.direct());
+        }
+        steps.set(GenerationStep.Decoration.UNDERGROUND_ORES.ordinal(), HolderSet.direct(feature));
+        Field features = BiomeGenerationSettings.class.getDeclaredField("features");
+        features.setAccessible(true);
+        features.set(settings, List.copyOf(steps));
+    }
+
+    /**
+     * What a Fabric weather modification does: it replaces the registered biome's climate settings.
+     */
+    private static void warmInPlace(Biome biome) throws ReflectiveOperationException {
+        Constructor<Biome.ClimateSettings> climate = Biome.ClimateSettings.class.getDeclaredConstructor(
+                boolean.class, float.class, Biome.TemperatureModifier.class, float.class);
+        climate.setAccessible(true);
+        Field climateSettings = Biome.class.getDeclaredField("climateSettings");
+        climateSettings.setAccessible(true);
+        climateSettings.set(biome, climate.newInstance(true, 0.1F, Biome.TemperatureModifier.NONE, 0.4F));
+    }
+}