diff --git a/src/main/java/dev/architectury/loom/neoforge/LaunchHandlerPatcher.java b/src/main/java/dev/architectury/loom/neoforge/LaunchHandlerPatcher.java
new file mode 100644
index 000000000..1429499a3
--- /dev/null
+++ b/src/main/java/dev/architectury/loom/neoforge/LaunchHandlerPatcher.java
@@ -0,0 +1,40 @@
+package dev.architectury.loom.neoforge;
+
+import org.objectweb.asm.ClassVisitor;
+import org.objectweb.asm.MethodVisitor;
+import org.objectweb.asm.Opcodes;
+
+/*
+ * Patches the Minecraft.class check in FML's CommonUserdevLaunchHandler
+ * to refer to a class that is found in any mapping set (Main.class).
+ *
+ * See https://github.com/architectury/architectury-loom/issues/212
+ */
+public final class LaunchHandlerPatcher extends ClassVisitor {
+	private static final String INPUT_CLASS_FILE = "net/minecraft/client/Minecraft.class";
+	private static final String OUTPUT_CLASS_FILE = "net/minecraft/client/main/Main.class";
+
+	public LaunchHandlerPatcher(ClassVisitor next) {
+		super(Opcodes.ASM9, next);
+	}
+
+	@Override
+	public MethodVisitor visitMethod(int access, String name, String descriptor, String signature, String[] exceptions) {
+		return new MethodPatcher(super.visitMethod(access, name, descriptor, signature, exceptions));
+	}
+
+	private static final class MethodPatcher extends MethodVisitor {
+		MethodPatcher(MethodVisitor next) {
+			super(Opcodes.ASM9, next);
+		}
+
+		@Override
+		public void visitLdcInsn(Object value) {
+			if (INPUT_CLASS_FILE.equals(value)) {
+				value = OUTPUT_CLASS_FILE;
+			}
+
+			super.visitLdcInsn(value);
+		}
+	}
+}
diff --git a/src/main/java/dev/architectury/loom/util/ClassVisitorUtil.java b/src/main/java/dev/architectury/loom/util/ClassVisitorUtil.java
new file mode 100644
index 000000000..f0e0003ac
--- /dev/null
+++ b/src/main/java/dev/architectury/loom/util/ClassVisitorUtil.java
@@ -0,0 +1,31 @@
+package dev.architectury.loom.util;
+
+import java.io.IOException;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.util.Arrays;
+import java.util.function.UnaryOperator;
+
+import org.objectweb.asm.ClassReader;
+import org.objectweb.asm.ClassVisitor;
+import org.objectweb.asm.ClassWriter;
+
+import net.fabricmc.loom.util.ExceptionUtil;
+
+public final class ClassVisitorUtil {
+	public static void rewriteClassFile(Path path, UnaryOperator<ClassVisitor> visitorFactory) throws IOException {
+		try {
+			final byte[] inputBytes = Files.readAllBytes(path);
+			final var reader = new ClassReader(inputBytes);
+			final var writer = new ClassWriter(0);
+			reader.accept(visitorFactory.apply(writer), 0);
+			final byte[] outputBytes = writer.toByteArray();
+
+			if (!Arrays.equals(inputBytes, outputBytes)) {
+				Files.write(path, outputBytes);
+			}
+		} catch (IOException e) {
+			throw ExceptionUtil.createDescriptiveWrapper(IOException::new, "Failed to patch " + path, e);
+		}
+	}
+}
diff --git a/src/main/java/net/fabricmc/loom/configuration/providers/forge/ForgeLibrariesProvider.java b/src/main/java/net/fabricmc/loom/configuration/providers/forge/ForgeLibrariesProvider.java
index 6b56d81e7..31be3cfa9 100644
--- a/src/main/java/net/fabricmc/loom/configuration/providers/forge/ForgeLibrariesProvider.java
+++ b/src/main/java/net/fabricmc/loom/configuration/providers/forge/ForgeLibrariesProvider.java
@@ -1,7 +1,7 @@
 /*
  * This file is part of fabric-loom, licensed under the MIT License (MIT).
  *
- * Copyright (c) 2022-2023 FabricMC
+ * Copyright (c) 2022-2024 FabricMC
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal
@@ -32,6 +32,8 @@
 import java.util.List;
 
 import com.google.common.hash.Hashing;
+import dev.architectury.loom.neoforge.LaunchHandlerPatcher;
+import dev.architectury.loom.util.ClassVisitorUtil;
 import org.gradle.api.Project;
 import org.gradle.api.artifacts.Dependency;
 import org.gradle.api.artifacts.ModuleDependency;
@@ -60,6 +62,10 @@ public class ForgeLibrariesProvider {
 	private static final String FANCYML_LOADER_GROUP = "net.neoforged.fancymodloader";
 	private static final String FANCYML_LOADER_NAME = "loader";
 
+	private static final String FORGE_OBJECT_HOLDER_FILE = "net/minecraftforge/fml/common/asm/ObjectHolderDefinalize.class";
+	private static final String NEOFORGE_OBJECT_HOLDER_FILE = "net/neoforged/fml/common/asm/ObjectHolderDefinalize.class";
+	private static final String NEOFORGE_LAUNCH_HANDLER_FILE = "net/neoforged/fml/loading/targets/CommonUserdevLaunchHandler.class";
+
 	public static void provide(MappingConfiguration mappingConfiguration, Project project) throws Exception {
 		LoomGradleExtension extension = LoomGradleExtension.get(project);
 		final List<Dependency> dependencies = new ArrayList<>();
@@ -166,13 +172,17 @@ private static Object remapFmlLoader(Project project, ResolvedArtifact artifact,
 				Path path = fs.get().getPath("META-INF/services/cpw.mods.modlauncher.api.INameMappingService");
 				Files.deleteIfExists(path);
 
-				if (Files.exists(fs.get().getPath("net/minecraftforge/fml/common/asm/ObjectHolderDefinalize.class"))) {
+				if (Files.exists(fs.get().getPath(FORGE_OBJECT_HOLDER_FILE))) {
 					remapObjectHolder(project, outputJar, mappingConfiguration);
 				}
 
-				if (Files.exists(fs.getPath("net/neoforged/fml/common/asm/ObjectHolderDefinalize.class"))) {
+				if (Files.exists(fs.getPath(NEOFORGE_OBJECT_HOLDER_FILE))) {
 					remapNeoForgeObjectHolder(project, outputJar, mappingConfiguration);
 				}
+
+				if (Files.exists(fs.getPath(NEOFORGE_LAUNCH_HANDLER_FILE))) {
+					ClassVisitorUtil.rewriteClassFile(fs.getPath(NEOFORGE_LAUNCH_HANDLER_FILE), LaunchHandlerPatcher::new);
+				}
 			}
 
 			// Copy sources when not running under CI.