diff --git a/filament/src/main/java/net/fabricmc/filament/mappingpoet/ClassBuilder.java b/filament/src/main/java/net/fabricmc/filament/mappingpoet/ClassBuilder.java
index 1792605cec..3dbf661e3e 100644
--- a/filament/src/main/java/net/fabricmc/filament/mappingpoet/ClassBuilder.java
+++ b/filament/src/main/java/net/fabricmc/filament/mappingpoet/ClassBuilder.java
@@ -42,6 +42,7 @@ public class ClassBuilder {
 
 	private Signatures.ClassSignature signature;
 	private boolean enumClass;
+	private boolean instanceInner = false;
 
 	public ClassBuilder(MappingsStore mappings, ClassNode classNode, Function<String, Collection<String>> superGetter) {
 		this.mappings = mappings;
@@ -50,9 +51,12 @@ public class ClassBuilder {
 		this.builder = setupBuilder();
 		addInterfaces();
 		addDirectAnnotations();
+		addJavaDoc();
+	}
+
+	public void addMembers() {
 		addMethods();
 		addFields();
-		addJavaDoc();
 	}
 
 	public static ClassName parseInternalName(String internalName) {
@@ -150,6 +154,7 @@ public class ClassBuilder {
 			if (method.name.equals("<clinit>")) {
 				continue;
 			}
+			int formalParamStartIndex = 0;
 			if (enumClass) {
 				// Skip enum sugar methods
 				if (method.name.equals("values") && method.desc.equals("()[L" + classNode.name + ";")) {
@@ -158,8 +163,16 @@ public class ClassBuilder {
 				if (method.name.equals("valueOf") && method.desc.equals("(Ljava/lang/String;)L" + classNode.name + ";")) {
 					continue;
 				}
+				if (method.name.equals("<init>")) {
+					formalParamStartIndex = 2; // 0 String 1 int
+				}
 			}
-			builder.addMethod(new MethodBuilder(mappings, classNode, method, superGetter).build());
+			if (instanceInner) {
+				if (method.name.equals("<init>")) {
+					formalParamStartIndex = 1; // 0 this$0
+				}
+			}
+			builder.addMethod(new MethodBuilder(mappings, classNode, method, superGetter, formalParamStartIndex).build());
 		}
 	}
 
@@ -202,6 +215,7 @@ public class ClassBuilder {
 			classBuilder.builder.addModifiers(javax.lang.model.element.Modifier.STATIC);
 		} else {
 			classBuilder.builder.addModifiers(new ModifierBuilder(innerClassNode.access).getModifiers(classBuilder.enumClass ? ModifierBuilder.Type.ENUM : ModifierBuilder.Type.CLASS));
+			if (!Modifier.isStatic(innerClassNode.access)) classBuilder.instanceInner = true;
 		}
 		innerClasses.add(classBuilder);
 	}
diff --git a/filament/src/main/java/net/fabricmc/filament/mappingpoet/Main.java b/filament/src/main/java/net/fabricmc/filament/mappingpoet/Main.java
index ddcd158b77..98d6f690f6 100644
--- a/filament/src/main/java/net/fabricmc/filament/mappingpoet/Main.java
+++ b/filament/src/main/java/net/fabricmc/filament/mappingpoet/Main.java
@@ -16,11 +16,6 @@
 
 package net.fabricmc.mappingpoet;
 
-import com.squareup.javapoet.JavaFile;
-import com.squareup.javapoet.TypeSpec;
-import org.objectweb.asm.ClassReader;
-import org.objectweb.asm.tree.ClassNode;
-
 import java.io.File;
 import java.io.IOException;
 import java.io.InputStream;
@@ -36,11 +31,15 @@ import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
 import java.util.function.BiConsumer;
-import java.util.function.Consumer;
 import java.util.function.Function;
 import java.util.jar.JarEntry;
 import java.util.jar.JarFile;
 
+import com.squareup.javapoet.JavaFile;
+import com.squareup.javapoet.TypeSpec;
+import org.objectweb.asm.ClassReader;
+import org.objectweb.asm.tree.ClassNode;
+
 public class Main {
 
 	public static void main(String[] args) {
@@ -111,7 +110,7 @@ public class Main {
 					continue;
 				}
 
-				try(InputStream is = jarFile.getInputStream(entry)) {
+				try (InputStream is = jarFile.getInputStream(entry)) {
 					ClassReader reader = new ClassReader(is);
 					ClassNode classNode = new ClassNode();
 					reader.accept(classNode, 0);
@@ -139,7 +138,7 @@ public class Main {
 		Function<String, Collection<String>> superGetter = k -> supers.getOrDefault(k, Collections.emptyList());
 		classes.forEach(node -> classNodeConsumer.accept(superGetter, node));
 	}
-	
+
 	private static boolean isDigit(char ch) {
 		return ch >= '0' && ch <= '9';
 	}
@@ -151,8 +150,10 @@ public class Main {
 			int lastSearch = name.length();
 			while (lastSearch != -1) {
 				lastSearch = name.lastIndexOf('$', lastSearch - 1);
-				if (isDigit(name.charAt(lastSearch + 1))) // names starting with digit is illegal java
+				// names starting with digit is illegal java
+				if (isDigit(name.charAt(lastSearch + 1))) {
 					return;
+				}
 			}
 		}
 
@@ -166,6 +167,7 @@ public class Main {
 			existingClasses.get(parentClass).addInnerClass(classBuilder);
 		}
 
+		classBuilder.addMembers();
 		existingClasses.put(name, classBuilder);
 
 	}
diff --git a/filament/src/main/java/net/fabricmc/filament/mappingpoet/MethodBuilder.java b/filament/src/main/java/net/fabricmc/filament/mappingpoet/MethodBuilder.java
index fa256de348..7983066569 100644
--- a/filament/src/main/java/net/fabricmc/filament/mappingpoet/MethodBuilder.java
+++ b/filament/src/main/java/net/fabricmc/filament/mappingpoet/MethodBuilder.java
@@ -21,6 +21,7 @@ import java.util.Arrays;
 import java.util.Collection;
 import java.util.Collections;
 import java.util.HashSet;
+import java.util.Iterator;
 import java.util.List;
 import java.util.Map;
 import java.util.Set;
@@ -50,14 +51,16 @@ public class MethodBuilder {
 	private final MethodNode methodNode;
 	private final MethodSpec.Builder builder;
 	private final Function<String, Collection<String>> superGetter;
+	private final int formalParamStartIndex;
 
 	private Signatures.MethodSignature signature;
 
-	public MethodBuilder(MappingsStore mappings, ClassNode classNode, MethodNode methodNode, Function<String, Collection<String>> superGetter) {
+	public MethodBuilder(MappingsStore mappings, ClassNode classNode, MethodNode methodNode, Function<String, Collection<String>> superGetter, int formalParamStartIndex) {
 		this.mappings = mappings;
 		this.classNode = classNode;
 		this.methodNode = methodNode;
 		this.superGetter = superGetter;
+		this.formalParamStartIndex = formalParamStartIndex;
 		this.builder = createBuilder();
 		addJavaDoc();
 		addDirectAnnotations();
@@ -184,11 +187,7 @@ public class MethodBuilder {
 		List<ParamType> paramTypes = new ArrayList<>();
 		boolean instanceMethod = !builder.modifiers.contains(Modifier.STATIC);
 		Set<String> usedParamNames = new HashSet<>(RESERVED_KEYWORDS);
-		if (signature != null) {
-			getGenericParams(paramTypes, instanceMethod, usedParamNames);
-		} else {
-			getDescParams(paramTypes, instanceMethod, usedParamNames);
-		}
+		getParams(paramTypes, instanceMethod, usedParamNames);
 
 		List<AnnotationNode>[] visibleParameterAnnotations = methodNode.visibleParameterAnnotations;
 		List<AnnotationNode>[] invisibleParameterAnnotations = methodNode.invisibleParameterAnnotations;
@@ -206,20 +205,10 @@ public class MethodBuilder {
 		}
 	}
 
-	private void getGenericParams(List<ParamType> paramTypes, boolean instance, Set<String> usedParamNames) {
-		int slot = instance ? 1 : 0;
-		for (TypeName each : signature.parameters) {
-			paramTypes.add(new ParamType(mappings.getParamNameAndDoc(superGetter, new EntryTriple(classNode.name, methodNode.name, methodNode.desc), slot), each, usedParamNames, slot));
-			slot++;
-			if (each.equals(TypeName.DOUBLE) || each.equals(TypeName.LONG)) {
-				slot++;
-			}
-		}
-	}
-
-	private void getDescParams(List<ParamType> paramTypes, boolean instance, Set<String> usedParamNames) {
+	private void getParams(List<ParamType> paramTypes, boolean instance, Set<String> usedParamNames) {
 		int slot = instance ? 1 : 0;
 		final String desc = methodNode.desc;
+		int paramIndex = 0;
 		int index = 0;
 
 		if (desc.charAt(index) != '(') {
@@ -227,16 +216,23 @@ public class MethodBuilder {
 		}
 		index++; // consume '('
 
+		Iterator<TypeName> signatureParamIterator = signature == null ? Collections.emptyIterator() : signature.parameters.iterator();
 		while (desc.charAt(index) != ')') {
 			Map.Entry<Integer, TypeName> parsedParam = FieldBuilder.parseType(desc, index);
 			index = parsedParam.getKey();
 			TypeName paramType = parsedParam.getValue();
 
-			paramTypes.add(new ParamType(mappings.getParamNameAndDoc(superGetter, new EntryTriple(classNode.name, methodNode.name, methodNode.desc), slot), paramType, usedParamNames, slot));
+			if (paramIndex >= formalParamStartIndex) { // skip guessed synthetic/implicit params
+				if (signatureParamIterator.hasNext()) {
+					paramType = signatureParamIterator.next();
+				}
+				paramTypes.add(new ParamType(mappings.getParamNameAndDoc(superGetter, new EntryTriple(classNode.name, methodNode.name, methodNode.desc), slot), paramType, usedParamNames, slot));
+			}
 			slot++;
 			if (paramType.equals(TypeName.DOUBLE) || paramType.equals(TypeName.LONG)) {
 				slot++;
 			}
+			paramIndex++;
 		}
 		/* bruh, we don't care about return type
 		index++; // consume ')'