diff --git a/src/main/java/de/dhbwstuttgart/bytecode/funN/FunNGenerator.java b/src/main/java/de/dhbwstuttgart/bytecode/funN/FunNGenerator.java
index 83ed622d..903fe6d9 100644
--- a/src/main/java/de/dhbwstuttgart/bytecode/funN/FunNGenerator.java
+++ b/src/main/java/de/dhbwstuttgart/bytecode/funN/FunNGenerator.java
@@ -174,6 +174,8 @@ public final class FunNGenerator implements FunNUtilities{
         return new RefType(new JavaClassName(getSpecializedClassName(argumentTypes, returnType)),
                 Stream
                         .concat(argumentTypes.stream(), Stream.of(returnType))
+                        .filter(t -> t instanceof GenericRefType ||
+                                t instanceof TypePlaceholder)
                         .collect(Collectors.toList()),null);
     }
 }
diff --git a/src/test/java/bytecode/funN/FunNGeneratorTest.java b/src/test/java/bytecode/funN/FunNGeneratorTest.java
index 2b53d135..b1e14cf0 100644
--- a/src/test/java/bytecode/funN/FunNGeneratorTest.java
+++ b/src/test/java/bytecode/funN/FunNGeneratorTest.java
@@ -73,13 +73,13 @@ public class FunNGeneratorTest {
     @Test
     public void signature_IntInt(){
         var classSignature = funNGenerator.getSpecializedSignature(Arrays.asList(integerType), integerType);
-        assertEquals("LFun1$$Ljava$lang$Integer$_$Ljava$lang$Integer$_$<Ljava/lang/Integer;Ljava/lang/Integer;>;", classSignature);
+        assertEquals("LFun1$$Ljava$lang$Integer$_$Ljava$lang$Integer$_$;", classSignature);
     }
 
     @Test
     public void signature_IntT(){
         var classSignature = funNGenerator.getSpecializedSignature(Arrays.asList(integerType), genericT);
-        assertEquals("LFun1$$Ljava$lang$Integer$_$LT$_$<Ljava/lang/Integer;TT;>;", classSignature);
+        assertEquals("LFun1$$Ljava$lang$Integer$_$LT$_$<TT;>;", classSignature);
     }
 
     @Test