diff --git a/src/main/java/de/dhbwstuttgart/bytecode/Codegen.java b/src/main/java/de/dhbwstuttgart/bytecode/Codegen.java
index d9b41787..7403f2e1 100644
--- a/src/main/java/de/dhbwstuttgart/bytecode/Codegen.java
+++ b/src/main/java/de/dhbwstuttgart/bytecode/Codegen.java
@@ -705,11 +705,15 @@ public class Codegen {
         } else {
             var name = "lambda$" + lambdaCounter++;
             var parameters = new ArrayList<>(lambda.captures());
-            parameters.addAll(lambda.params());
+            parameters.addAll(lambda.params().stream()
+                    .map(param -> param.type() instanceof TargetGenericType ? new MethodParameter(TargetType.Object, param.name()) : param)
+                    .toList());
 
             impl = new TargetMethod(
                     0, name, Set.of(), Set.of(),
-                    parameters, lambda.returnType(), lambda.block()
+                    parameters,
+                    lambda.returnType() instanceof TargetGenericType ? TargetType.Object : lambda.returnType(),
+                    lambda.block()
             );
             generateMethod(impl);
             lambdas.put(lambda, impl);
@@ -736,7 +740,9 @@ public class Codegen {
 
         var params = new ArrayList<TargetType>();
         params.add(new TargetRefType(clazz.qualifiedName()));
-        params.addAll(lambda.captures().stream().map(MethodParameter::type).toList());
+        params.addAll(lambda.captures().stream()
+                .map(MethodParameter::type)
+                .toList());
 
         var descriptor = TargetMethod.getDescriptor(lambda.type(), params.toArray(TargetType[]::new));
         mv.visitVarInsn(ALOAD, 0);