diff --git a/build.gradle b/build.gradle
index 4e48d53d5..59a805450 100644
--- a/build.gradle
+++ b/build.gradle
@@ -193,7 +193,7 @@ dependencies {
 	implementation libs.night.config.toml
 
 	// Legacy Forge patches
-	implementation libs.lzma
+	implementation libs.xz
 
 	// Testing
 	testImplementation(gradleTestKit())
diff --git a/gradle/libs.versions.toml b/gradle/libs.versions.toml
index 1d5e27835..c378d3d88 100644
--- a/gradle/libs.versions.toml
+++ b/gradle/libs.versions.toml
@@ -30,7 +30,7 @@ forge-diffpatch = "2.0.7"
 night-config = "3.6.6"
 datafixerupper = "6.0.8"
 at = "1.0.1"
-lzma = "1.3"
+xz = "1.8"
 
 [libraries]
 # Loom compile libraries
@@ -65,7 +65,7 @@ forge-diffpatch = { module = "net.minecraftforge:DiffPatch", version.ref = "forg
 night-config-toml = { module = "com.electronwill.night-config:toml", version.ref = "night-config" }
 datafixerupper = { module = "com.mojang:datafixerupper", version.ref = "datafixerupper" }
 at = { module = "dev.architectury:at", version.ref = "at" }
-lzma = { module = "com.github.jponge:lzma-java", version.ref = "lzma" }
+xz = { module = "org.tukaani:xz", version.ref = "xz" }
 
 [plugins]
 kotlin = { id = "org.jetbrains.kotlin.jvm", version.ref = "kotlin" }
diff --git a/src/main/java/net/fabricmc/loom/LoomGradleExtension.java b/src/main/java/net/fabricmc/loom/LoomGradleExtension.java
index 62888f11c..cc6c104e5 100644
--- a/src/main/java/net/fabricmc/loom/LoomGradleExtension.java
+++ b/src/main/java/net/fabricmc/loom/LoomGradleExtension.java
@@ -176,8 +176,12 @@ default boolean isForgeLikeAndNotOfficial() {
 		return isForgeLike() && !getMcpConfigProvider().isOfficial();
 	}
 
+	default int getForgeSpec() {
+		return getForgeUserdevProvider().getForgeSpec();
+	}
+
 	default boolean isLegacyForge() {
-		return isForge() && getForgeUserdevProvider().isLegacyForge();
+		return isForge() && getForgeSpec() <= 1;
 	}
 
 	default boolean isModernForge() {
diff --git a/src/main/java/net/fabricmc/loom/configuration/CompileConfiguration.java b/src/main/java/net/fabricmc/loom/configuration/CompileConfiguration.java
index b048f5e21..a687f0ba1 100644
--- a/src/main/java/net/fabricmc/loom/configuration/CompileConfiguration.java
+++ b/src/main/java/net/fabricmc/loom/configuration/CompileConfiguration.java
@@ -226,13 +226,13 @@ private synchronized void setupMinecraft(ConfigContext configContext) throws Exc
 		// but before MinecraftPatchedProvider.provide.
 		setupDependencyProviders(project, extension);
 
-		if (extension.isLegacyForge()) {
+		if (extension.getForgeSpec() <= 2) {
 			extension.setIntermediateMappingsProvider(GeneratedIntermediateMappingsProvider.class, provider -> {
 				provider.minecraftProvider = minecraftProvider;
 			});
 		}
 
-		if (extension.isForgeLike() && !extension.isLegacyForge()) {
+		if (extension.isForgeLike() && extension.getForgeSpec() > 2) {
 			// Excluded on legacy forge because it pulls in a log4j-api version newer than what forge wants and we don't
 			// need it anyway
 			project.getDependencies().add(Constants.Configurations.FORGE_EXTRA, LoomVersions.UNPROTECT.mavenNotation());
diff --git a/src/main/java/net/fabricmc/loom/configuration/providers/forge/ForgeMigratedMappingConfiguration.java b/src/main/java/net/fabricmc/loom/configuration/providers/forge/ForgeMigratedMappingConfiguration.java
index ee4c568be..1c0bcd6f6 100644
--- a/src/main/java/net/fabricmc/loom/configuration/providers/forge/ForgeMigratedMappingConfiguration.java
+++ b/src/main/java/net/fabricmc/loom/configuration/providers/forge/ForgeMigratedMappingConfiguration.java
@@ -53,7 +53,7 @@ public ForgeMigratedMappingConfiguration(String mappingsIdentifier, Path mapping
 	protected void manipulateMappings(Project project, Path mappingsJar) throws IOException {
 		LoomGradleExtension extension = LoomGradleExtension.get(project);
 
-		if (extension.isLegacyForge()) {
+		if (extension.getForgeSpec() <= 2) {
 			// Legacy forge patches are in official namespace, so if the type of a field is changed by them, then that
 			// is effectively a new field and not traceable to any mapping. Therefore this does not apply to it.
 			return;
diff --git a/src/main/java/net/fabricmc/loom/configuration/providers/forge/ForgeUserdevProvider.java b/src/main/java/net/fabricmc/loom/configuration/providers/forge/ForgeUserdevProvider.java
index cefad0de2..6f22f72be 100644
--- a/src/main/java/net/fabricmc/loom/configuration/providers/forge/ForgeUserdevProvider.java
+++ b/src/main/java/net/fabricmc/loom/configuration/providers/forge/ForgeUserdevProvider.java
@@ -53,7 +53,7 @@ public class ForgeUserdevProvider extends DependencyProvider {
 	private JsonObject json;
 	private UserdevConfig config;
 	Path joinedPatches;
-	private Boolean isLegacyForge;
+	private Integer forgeSpec;
 
 	public ForgeUserdevProvider(Project project) {
 		super(project);
@@ -88,10 +88,13 @@ public void provide(DependencyInfo dependency) throws Exception {
 
 		try (Reader reader = Files.newBufferedReader(configJson)) {
 			json = new Gson().fromJson(reader, JsonObject.class);
-			isLegacyForge = !json.has("mcp");
+			// Some Forge versions for 1.13.2 specify mcp, but have spec=1. We just "hack" this here.
+			forgeSpec = json.has("mcp") ? Math.max(2, json.get("spec").getAsInt()) : 1;
 
-			if (isLegacyForge) {
+			if (forgeSpec <= 1) {
 				json = createManifestFromForgeGradle2(dependency, json);
+			} else if (forgeSpec <= 2) {
+				addLegacyMCPRepo();
 			}
 
 			config = UserdevConfig.CODEC.parse(JsonOps.INSTANCE, json)
@@ -106,7 +109,7 @@ public void provide(DependencyInfo dependency) throws Exception {
 
 		addDependency(config.universal(), Constants.Configurations.FORGE_UNIVERSAL);
 
-		if (!isLegacyForge && Files.notExists(joinedPatches)) {
+		if (forgeSpec >= 2 && Files.notExists(joinedPatches)) {
 			Files.write(joinedPatches, ZipUtils.unpack(userdevJar.toPath(), config.binpatches()));
 		}
 	}
@@ -210,12 +213,12 @@ private void addLegacyMCPRepo() {
 		});
 	}
 
-	public boolean isLegacyForge() {
-		if (isLegacyForge == null) {
+	public int getForgeSpec() {
+		if (forgeSpec == null) {
 			throw new IllegalArgumentException("Not yet resolved.");
 		}
 
-		return isLegacyForge;
+		return forgeSpec;
 	}
 
 	public File getUserdevJar() {
diff --git a/src/main/java/net/fabricmc/loom/configuration/providers/forge/PatchProvider.java b/src/main/java/net/fabricmc/loom/configuration/providers/forge/PatchProvider.java
index 313709a55..239d34e27 100644
--- a/src/main/java/net/fabricmc/loom/configuration/providers/forge/PatchProvider.java
+++ b/src/main/java/net/fabricmc/loom/configuration/providers/forge/PatchProvider.java
@@ -43,12 +43,11 @@
 import java.util.jar.JarOutputStream;
 import java.util.zip.ZipEntry;
 
-import lzma.sdk.lzma.Decoder;
-import lzma.sdk.lzma.Encoder;
-import lzma.streams.LzmaInputStream;
-import lzma.streams.LzmaOutputStream;
 import org.apache.commons.io.IOUtils;
 import org.gradle.api.Project;
+import org.tukaani.xz.LZMA2Options;
+import org.tukaani.xz.LZMAInputStream;
+import org.tukaani.xz.LZMAOutputStream;
 
 import net.fabricmc.loom.configuration.DependencyInfo;
 import net.fabricmc.loom.configuration.providers.forge.fg2.Pack200Provider;
@@ -99,12 +98,12 @@ private void init() {
 
 	private void splitAndConvertLegacyPatches(Path joinedLegacyPatches) throws IOException {
 		try (JarInputStream in = new JarInputStream(new ByteArrayInputStream(unpack200Lzma(joinedLegacyPatches)));
-				OutputStream clientFileOut = Files.newOutputStream(clientPatches, CREATE, TRUNCATE_EXISTING);
-				LzmaOutputStream clientLzmaOut = new LzmaOutputStream(clientFileOut, new Encoder());
-				JarOutputStream clientJarOut = new JarOutputStream(clientLzmaOut);
-				OutputStream serverFileOut = Files.newOutputStream(serverPatches, CREATE, TRUNCATE_EXISTING);
-				LzmaOutputStream serverLzmaOut = new LzmaOutputStream(serverFileOut, new Encoder());
-				JarOutputStream serverJarOut = new JarOutputStream(serverLzmaOut);
+			 OutputStream clientFileOut = Files.newOutputStream(clientPatches, CREATE, TRUNCATE_EXISTING);
+			 LZMAOutputStream clientLzmaOut = new LZMAOutputStream(clientFileOut, new LZMA2Options(), -1);
+			 JarOutputStream clientJarOut = new JarOutputStream(clientLzmaOut);
+			 OutputStream serverFileOut = Files.newOutputStream(serverPatches, CREATE, TRUNCATE_EXISTING);
+			 LZMAOutputStream serverLzmaOut = new LZMAOutputStream(serverFileOut, new LZMA2Options(), -1);
+			 JarOutputStream serverJarOut = new JarOutputStream(serverLzmaOut)
 		) {
 			for (JarEntry entry; (entry = in.getNextJarEntry()) != null;) {
 				String name = entry.getName();
@@ -153,7 +152,7 @@ private byte[] unpack200(InputStream in) throws IOException {
 	}
 
 	private byte[] unpack200Lzma(InputStream in) throws IOException {
-		try (LzmaInputStream lzmaIn = new LzmaInputStream(in, new Decoder())) {
+		try (LZMAInputStream lzmaIn = new LZMAInputStream(in)) {
 			return unpack200(lzmaIn);
 		}
 	}
diff --git a/src/test/groovy/net/fabricmc/loom/test/integration/forge/ForgeTest.groovy b/src/test/groovy/net/fabricmc/loom/test/integration/forge/ForgeTest.groovy
index 170c93d23..43e566e0f 100644
--- a/src/test/groovy/net/fabricmc/loom/test/integration/forge/ForgeTest.groovy
+++ b/src/test/groovy/net/fabricmc/loom/test/integration/forge/ForgeTest.groovy
@@ -65,6 +65,7 @@ class ForgeTest extends Specification implements GradleProjectTestTrait {
 		'1.16.5'  | '36.2.4'     | '8'         | '"de.oceanlabs.mcp:mcp_snapshot:20210309-1.16.5"'
 		'1.14.4'  | "28.2.23"    | '8'         | "loom.officialMojangMappings()"
 		'1.14.4'  | "28.2.23"    | '8'         | '"net.fabricmc:yarn:1.14.4+build.18:v2"'
+		'1.13.2'  | "25.0.223"   | '8'         | '"de.oceanlabs.mcp:mcp_stable:47-1.13.2"'
 		'1.12.2'  | "14.23.0.2486" | '8'       | '"de.oceanlabs.mcp:mcp_snapshot:20170615-1.12"'
 		'1.8.9'   | "11.15.1.2318-1.8.9" | '8' | '"de.oceanlabs.mcp:mcp_stable:22-1.8.9"'
 	}