diff --git a/build.gradle b/build.gradle
index 5a9873f..ea0753c 100644
--- a/build.gradle
+++ b/build.gradle
@@ -2,6 +2,7 @@ plugins {
 	id "java"
 	id "java-library"
 	id "maven-publish"
+	id "eclipse"
 	id "net.minecrell.licenser" version "0.4.1"
 }
 
@@ -25,6 +26,7 @@ repositories {
 		url = "https://maven.fabricmc.net/"
 		content {
 			includeGroup("net.fabricmc") // I'd like to deprecate procyon, so we don't need to maintain it
+			includeGroup("cuchaz")
 		}
 	}
 }
diff --git a/src/main/java/net/fabricmc/stitch/merge/ClassMerger.java b/src/main/java/net/fabricmc/stitch/merge/ClassMerger.java
index 738a195..a92aa63 100644
--- a/src/main/java/net/fabricmc/stitch/merge/ClassMerger.java
+++ b/src/main/java/net/fabricmc/stitch/merge/ClassMerger.java
@@ -23,10 +23,14 @@
 import java.util.*;
 
 public class ClassMerger {
+    // Fabric
     private static final String SIDE_DESCRIPTOR = "Lnet/fabricmc/api/EnvType;";
     private static final String ITF_DESCRIPTOR = "Lnet/fabricmc/api/EnvironmentInterface;";
     private static final String ITF_LIST_DESCRIPTOR = "Lnet/fabricmc/api/EnvironmentInterfaces;";
     private static final String SIDED_DESCRIPTOR = "Lnet/fabricmc/api/Environment;";
+    // Quilt
+    private static final String QUILT_CLIENT_DESC = "Lorg/quiltmc/loader/api/minecraft/ClientOnly;";
+    private static final String QUILT_SERVER_DESC = "Lorg/quiltmc/loader/api/minecraft/DedicatedServerOnly;";
 
     private abstract class Merger<T> {
         private final Map<String, T> entriesClient, entriesServer;
@@ -89,24 +93,41 @@ private static void visitItfAnnotation(AnnotationVisitor av, String side, List<S
 
     public static class SidedClassVisitor extends ClassVisitor {
         private final String side;
+        private boolean useQuilt = true;
 
         public SidedClassVisitor(int api, ClassVisitor cv, String side) {
             super(api, cv);
             this.side = side;
         }
 
+        public SidedClassVisitor setUseQuiltAnnotations(boolean use) {
+            useQuilt = use;
+            return this;
+        }
+
         @Override
         public void visitEnd() {
-            AnnotationVisitor av = cv.visitAnnotation(SIDED_DESCRIPTOR, true);
-            visitSideAnnotation(av, side);
+            if (useQuilt) {
+                cv.visitAnnotation("CLIENT".equals(side) ? QUILT_CLIENT_DESC : QUILT_SERVER_DESC, true);
+            } else {
+                AnnotationVisitor av = cv.visitAnnotation(SIDED_DESCRIPTOR, true);
+                visitSideAnnotation(av, side);
+            }
             super.visitEnd();
         }
     }
 
+    private boolean useQuilt = true;
+
     public ClassMerger() {
 
     }
 
+    public ClassMerger setUseQuiltAnnotations(boolean use) {
+        useQuilt = use;
+        return this;
+    }
+
     public byte[] merge(byte[] classClient, byte[] classServer) {
         ClassReader readerC = new ClassReader(classClient);
         ClassReader readerS = new ClassReader(classServer);
@@ -168,7 +189,22 @@ public byte[] merge(byte[] classClient, byte[] classServer) {
             }
         }
 
-        if (!clientItfs.isEmpty() || !serverItfs.isEmpty()) {
+        if (useQuilt) {
+            if (!clientItfs.isEmpty()) {
+            	for (String itf : clientItfs) {
+            		int ref = TypeReference.CLASS_EXTENDS | nodeOut.interfaces.indexOf(itf) << 8;
+            		nodeOut.visitTypeAnnotation(ref, null, QUILT_CLIENT_DESC, false);
+            	}
+            }
+
+            if (!serverItfs.isEmpty()) {
+            	for (String itf : serverItfs) {
+            		int ref = TypeReference.CLASS_EXTENDS | nodeOut.interfaces.indexOf(itf) << 8;
+            		nodeOut.visitTypeAnnotation(ref, null, QUILT_SERVER_DESC, false);
+            	}
+            }
+        
+        } else if (!clientItfs.isEmpty() || !serverItfs.isEmpty()) {
             AnnotationVisitor envInterfaces = nodeOut.visitAnnotation(ITF_LIST_DESCRIPTOR, false);
             AnnotationVisitor eiArray = envInterfaces.visitArray("value");
 
@@ -201,8 +237,12 @@ public String getName(FieldNode entry) {
 
             @Override
             public void applySide(FieldNode entry, String side) {
-                AnnotationVisitor av = entry.visitAnnotation(SIDED_DESCRIPTOR, false);
-                visitSideAnnotation(av, side);
+                if (useQuilt) {
+                    entry.visitAnnotation("CLIENT".equals(side) ? QUILT_CLIENT_DESC : QUILT_SERVER_DESC, false);
+                } else {
+                    AnnotationVisitor av = entry.visitAnnotation(SIDED_DESCRIPTOR, false);
+                    visitSideAnnotation(av, side);
+                }
             }
         }.merge(nodeOut.fields);
 
@@ -214,8 +254,12 @@ public String getName(MethodNode entry) {
 
             @Override
             public void applySide(MethodNode entry, String side) {
-                AnnotationVisitor av = entry.visitAnnotation(SIDED_DESCRIPTOR, false);
-                visitSideAnnotation(av, side);
+                if (useQuilt) {
+                    entry.visitAnnotation("CLIENT".equals(side) ? QUILT_CLIENT_DESC : QUILT_SERVER_DESC, false);
+                } else {
+                    AnnotationVisitor av = entry.visitAnnotation(SIDED_DESCRIPTOR, false);
+                    visitSideAnnotation(av, side);
+                }
             }
         }.merge(nodeOut.methods);
 
diff --git a/src/main/java/net/fabricmc/stitch/merge/JarMerger.java b/src/main/java/net/fabricmc/stitch/merge/JarMerger.java
index addf53b..5c142bc 100644
--- a/src/main/java/net/fabricmc/stitch/merge/JarMerger.java
+++ b/src/main/java/net/fabricmc/stitch/merge/JarMerger.java
@@ -47,13 +47,16 @@ public Entry(Path path, BasicFileAttributes metadata, byte[] data) {
         }
     }
 
-    private static final ClassMerger CLASS_MERGER = new ClassMerger();
+    private static final ClassMerger CLASS_MERGER_QUILT = new ClassMerger().setUseQuiltAnnotations(true);
+    private static final ClassMerger CLASS_MERGER_FABRIC = new ClassMerger().setUseQuiltAnnotations(false);
+
     private final StitchUtil.FileSystemDelegate inputClientFs, inputServerFs, outputFs;
     private final Path inputClient, inputServer;
     private final Map<String, Entry> entriesClient, entriesServer;
     private final Set<String> entriesAll;
     private boolean removeSnowmen = false;
     private boolean offsetSyntheticsParams = false;
+    private boolean useQuiltAnnotations = true;
 
     public JarMerger(File inputClient, File inputServer, File output) throws IOException {
         if (output.exists()) {
@@ -79,6 +82,10 @@ public void enableSyntheticParamsOffset() {
         offsetSyntheticsParams = true;
     }
 
+    public void setUseQuiltAnnotations(boolean use) {
+        useQuiltAnnotations = use;
+    }
+
     @Override
     public void close() throws IOException {
         inputClientFs.close();
@@ -170,7 +177,8 @@ public void merge() throws IOException {
                     result = entry1;
                 } else {
                     if (isClass) {
-                        result = new Entry(entry1.path, entry1.metadata, CLASS_MERGER.merge(entry1.data, entry2.data));
+                        ClassMerger classMerger = useQuiltAnnotations ? CLASS_MERGER_QUILT : CLASS_MERGER_FABRIC;
+                        result = new Entry(entry1.path, entry1.metadata, classMerger.merge(entry1.data, entry2.data));
                     } else {
                         // FIXME: More heuristics?
                         result = entry1;
@@ -195,7 +203,8 @@ public void merge() throws IOException {
                     ClassVisitor visitor = writer;
 
                     if (side != null) {
-                        visitor = new ClassMerger.SidedClassVisitor(StitchUtil.ASM_VERSION, visitor, side);
+                        visitor = new ClassMerger.SidedClassVisitor(StitchUtil.ASM_VERSION, visitor, side)
+                            .setUseQuiltAnnotations(useQuiltAnnotations);
                     }
 
                     if (removeSnowmen) {