diff --git a/src/main/java/net/fabricmc/loom/configuration/ide/RunConfig.java b/src/main/java/net/fabricmc/loom/configuration/ide/RunConfig.java
index 1f6f73ef..1783e903 100644
--- a/src/main/java/net/fabricmc/loom/configuration/ide/RunConfig.java
+++ b/src/main/java/net/fabricmc/loom/configuration/ide/RunConfig.java
@@ -138,10 +138,10 @@ public class RunConfig {
 		String environment = settings.getEnvironment();
 		SourceSet sourceSet = settings.getSource(project);
 
-		String defaultMain = settings.getDefaultMainClass();
+		String mainClass = settings.getMainClass().getOrNull();
 
-		if (defaultMain == null) {
-			throw new IllegalArgumentException("Run configuration '" + name + "' must specify 'defaultMainClass'");
+		if (mainClass == null) {
+			throw new IllegalArgumentException("Run configuration '" + name + "' must specify 'mainClass'");
 		}
 
 		if (configName == null) {
@@ -179,7 +179,7 @@ public class RunConfig {
 		// Custom parameters
 		runConfig.programArgs.addAll(settings.getProgramArgs());
 		runConfig.vmArgs.addAll(settings.getVmArgs());
-		runConfig.vmArgs.add("-Dfabric.dli.main=" + getMainClass(environment, extension, defaultMain));
+		runConfig.vmArgs.add("-Dfabric.dli.main=" + mainClass);
 		runConfig.environmentVariables = new HashMap<>();
 		runConfig.environmentVariables.putAll(settings.getEnvironmentVariables());
 		runConfig.projectName = project.getName();
@@ -245,7 +245,7 @@ public class RunConfig {
 		return sb.toString();
 	}
 
-	private static String getMainClass(String side, LoomGradleExtension extension, String defaultMainClass) {
+	static String getMainClass(String side, LoomGradleExtension extension, String defaultMainClass) {
 		InstallerData installerData = extension.getInstallerData();
 
 		if (installerData == null) {
diff --git a/src/main/java/net/fabricmc/loom/configuration/ide/RunConfigSettings.java b/src/main/java/net/fabricmc/loom/configuration/ide/RunConfigSettings.java
index 4447c152..82bfeeec 100644
--- a/src/main/java/net/fabricmc/loom/configuration/ide/RunConfigSettings.java
+++ b/src/main/java/net/fabricmc/loom/configuration/ide/RunConfigSettings.java
@@ -1,7 +1,7 @@
 /*
  * This file is part of fabric-loom, licensed under the MIT License (MIT).
  *
- * Copyright (c) 2021 FabricMC
+ * Copyright (c) 2021-2023 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
@@ -31,10 +31,12 @@ import java.util.Collection;
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
+import java.util.Objects;
 import java.util.function.Function;
 
 import org.gradle.api.Named;
 import org.gradle.api.Project;
+import org.gradle.api.provider.Property;
 import org.gradle.api.tasks.SourceSet;
 
 import net.fabricmc.loom.LoomGradleExtension;
@@ -74,6 +76,14 @@ public final class RunConfigSettings implements Named {
 	 */
 	private String defaultMainClass;
 
+	/**
+	 * The main class of the run configuration.
+	 *
+	 * <p>If unset, {@link #defaultMainClass} is used as the fallback, including the overwritten main class
+	 * from installer files.
+	 */
+	private final Property<String> mainClass;
+
 	/**
 	 * The source set getter, which obtains the source set from the given project.
 	 */
@@ -106,6 +116,11 @@ public final class RunConfigSettings implements Named {
 		this.project = project;
 		this.extension = LoomGradleExtension.get(project);
 		this.ideConfigGenerated = extension.isRootProject();
+		this.mainClass = project.getObjects().property(String.class).convention(project.provider(() -> {
+			Objects.requireNonNull(environment, "Run config " + baseName + " must specify environment");
+			Objects.requireNonNull(defaultMainClass, "Run config " + baseName + " must specify default main class");
+			return RunConfig.getMainClass(environment, extension, defaultMainClass);
+		}));
 
 		setSource(p -> {
 			final String sourceSetName = MinecraftSourceSets.get(p).getSourceSetForEnv(getEnvironment());
@@ -160,6 +175,16 @@ public final class RunConfigSettings implements Named {
 		this.defaultMainClass = defaultMainClass;
 	}
 
+	/**
+	 * The main class of the run configuration.
+	 *
+	 * <p>If unset, {@link #getDefaultMainClass defaultMainClass} is used as the fallback,
+	 * including the overwritten main class from installer files.
+	 */
+	public Property<String> getMainClass() {
+		return mainClass;
+	}
+
 	public String getRunDir() {
 		return runDir;
 	}
diff --git a/src/test/groovy/net/fabricmc/loom/test/integration/RunConfigTest.groovy b/src/test/groovy/net/fabricmc/loom/test/integration/RunConfigTest.groovy
index 38438e8b..770a7b23 100644
--- a/src/test/groovy/net/fabricmc/loom/test/integration/RunConfigTest.groovy
+++ b/src/test/groovy/net/fabricmc/loom/test/integration/RunConfigTest.groovy
@@ -1,7 +1,7 @@
 /*
  * This file is part of fabric-loom, licensed under the MIT License (MIT).
  *
- * Copyright (c) 2018-2021 FabricMC
+ * Copyright (c) 2018-2023 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
@@ -59,6 +59,22 @@ class RunConfigTest extends Specification implements GradleProjectTestTrait {
 		task << tasks * STANDARD_TEST_VERSIONS.size()
 	}
 
+	@Unroll
+	def "Custom main class (gradle #version)"() {
+		setup:
+		def gradle = gradleProject(project: "runconfigs", sharedFiles: true, version: version)
+
+		when:
+		def result = gradle.run(task: 'runCustomMain')
+
+		then:
+		result.task(':runCustomMain').outcome == SUCCESS
+		result.output.contains('hello custom main')
+
+		where:
+		version << STANDARD_TEST_VERSIONS
+	}
+
 	@RestoreSystemProperties
 	@Unroll
 	def "idea auto configuration (gradle #version)"() {
diff --git a/src/test/resources/projects/runconfigs/build.gradle b/src/test/resources/projects/runconfigs/build.gradle
index 3dfb3603..5e504e20 100644
--- a/src/test/resources/projects/runconfigs/build.gradle
+++ b/src/test/resources/projects/runconfigs/build.gradle
@@ -20,6 +20,11 @@ loom {
 			inherit testmodServer
 			vmArg "-Dfabric.autoTest"
 		}
+		customMain {
+			inherit server
+			name = 'Custom Main Class'
+			mainClass.set 'net.fabricmc.example.Main'
+		}
 	}
 
 	runConfigs.configureEach {
diff --git a/src/test/resources/projects/runconfigs/src/main/java/net/fabricmc/example/Main.java b/src/test/resources/projects/runconfigs/src/main/java/net/fabricmc/example/Main.java
new file mode 100644
index 00000000..3b79a86c
--- /dev/null
+++ b/src/test/resources/projects/runconfigs/src/main/java/net/fabricmc/example/Main.java
@@ -0,0 +1,10 @@
+package net.fabricmc.example;
+
+import net.fabricmc.loader.impl.launch.knot.KnotServer;
+
+public class Main {
+	public static void main(String[] args) {
+		System.out.println("hello custom main");
+		KnotServer.main(args);
+	}
+}