diff --git a/src/main/java/net/fabricmc/loom/LoomGradleExtension.java b/src/main/java/net/fabricmc/loom/LoomGradleExtension.java
index f458478..7c086f7 100644
--- a/src/main/java/net/fabricmc/loom/LoomGradleExtension.java
+++ b/src/main/java/net/fabricmc/loom/LoomGradleExtension.java
@@ -28,8 +28,11 @@ import java.io.File;
 import java.nio.file.Path;
 import java.util.ArrayList;
 import java.util.Collection;
+import java.util.Collections;
+import java.util.HashSet;
 import java.util.List;
 import java.util.Objects;
+import java.util.Set;
 import java.util.function.BiPredicate;
 import java.util.function.Function;
 import java.util.function.Supplier;
@@ -78,6 +81,7 @@ public class LoomGradleExtension {
 	private JsonObject installerJson;
 	private MappingSet[] srcMappingCache = new MappingSet[2];
 	private Mercury[] srcMercuryCache = new Mercury[2];
+	private Set<File> mixinMappings = Collections.synchronizedSet(new HashSet<>());
 
 	/**
 	 * Loom will generate a new genSources task (with a new name, based off of {@link LoomDecompiler#name()})
@@ -400,7 +404,15 @@ public class LoomGradleExtension {
 		return shareCaches;
 	}
 
-	public File getMixinMappings() {
-		return new File(getProjectBuildCache(), "mixin-map-" + getMinecraftProvider().getMinecraftVersion() + "-" + getMappingsProvider().mappingsVersion + ".tiny");
+	// Creates a new file each time its called, this is then held onto later when remapping the output jar
+	// Required as now when using parallel builds the old single file could be written by another sourceset compile task
+	public synchronized File getNextMixinMappings() {
+		File mixinMapping = new File(getProjectBuildCache(), "mixin-map-" + getMinecraftProvider().getMinecraftVersion() + "-" + getMappingsProvider().mappingsVersion + "." + mixinMappings.size() + ".tiny");
+		mixinMappings.add(mixinMapping);
+		return mixinMapping;
+	}
+
+	public Set<File> getAllMixinMappings() {
+		return Collections.unmodifiableSet(mixinMappings);
 	}
 }
diff --git a/src/main/java/net/fabricmc/loom/task/RemapJarTask.java b/src/main/java/net/fabricmc/loom/task/RemapJarTask.java
index 3129563..dca964c 100644
--- a/src/main/java/net/fabricmc/loom/task/RemapJarTask.java
+++ b/src/main/java/net/fabricmc/loom/task/RemapJarTask.java
@@ -99,15 +99,14 @@ public class RemapJarTask extends Jar {
 		);
 		Path[] classpath = classpathFiles.stream().map(File::toPath).filter((p) -> !input.equals(p) && Files.exists(p)).toArray(Path[]::new);
 
-		File mixinMapFile = extension.getMixinMappings();
-		Path mixinMapPath = mixinMapFile.toPath();
-
 		TinyRemapper.Builder remapperBuilder = TinyRemapper.newRemapper();
 
 		remapperBuilder = remapperBuilder.withMappings(TinyRemapperMappingsHelper.create(mappingsProvider.getMappings(), fromM, toM, false));
 
-		if (mixinMapFile.exists()) {
-			remapperBuilder = remapperBuilder.withMappings(TinyUtils.createTinyMappingProvider(mixinMapPath, fromM, toM));
+		for (File mixinMapFile : extension.getAllMixinMappings()) {
+			if (mixinMapFile.exists()) {
+				remapperBuilder = remapperBuilder.withMappings(TinyUtils.createTinyMappingProvider(mixinMapFile.toPath(), fromM, toM));
+			}
 		}
 
 		project.getLogger().lifecycle(":remapping " + input.getFileName());
@@ -194,11 +193,10 @@ public class RemapJarTask extends Jar {
 			jarRemapper.addMappings(TinyRemapperMappingsHelper.create(mappingsProvider.getMappings(), fromM, toM, false));
 		}
 
-		File mixinMapFile = extension.getMixinMappings();
-		Path mixinMapPath = mixinMapFile.toPath();
-
-		if (mixinMapFile.exists()) {
-			jarRemapper.addMappings(TinyUtils.createTinyMappingProvider(mixinMapPath, fromM, toM));
+		for (File mixinMapFile : extension.getAllMixinMappings()) {
+			if (mixinMapFile.exists()) {
+				jarRemapper.addMappings(TinyUtils.createTinyMappingProvider(mixinMapFile.toPath(), fromM, toM));
+			}
 		}
 
 		jarRemapper.scheduleRemap(input, output)
diff --git a/src/main/java/net/fabricmc/loom/util/mixin/AnnotationProcessorInvoker.java b/src/main/java/net/fabricmc/loom/util/mixin/AnnotationProcessorInvoker.java
index 09eedc6..13b237c 100644
--- a/src/main/java/net/fabricmc/loom/util/mixin/AnnotationProcessorInvoker.java
+++ b/src/main/java/net/fabricmc/loom/util/mixin/AnnotationProcessorInvoker.java
@@ -73,7 +73,7 @@ public abstract class AnnotationProcessorInvoker<T extends Task> {
 			LoomGradleExtension extension = project.getExtensions().getByType(LoomGradleExtension.class);
 			Map<String, String> args = new HashMap<String, String>() {{
 					put("inMapFileNamedIntermediary", extension.getMappingsProvider().tinyMappings.getCanonicalPath());
-					put("outMapFileNamedIntermediary", extension.getMixinMappings().getCanonicalPath());
+					put("outMapFileNamedIntermediary", extension.getNextMixinMappings().getCanonicalPath());
 					put("outRefMapFile", getRefmapDestination(task, extension));
 					put("defaultObfuscationEnv", "named:intermediary");
 				}};