diff --git a/src/main/java/de/dhbwstuttgart/target/generate/ASTToTargetAST.java b/src/main/java/de/dhbwstuttgart/target/generate/ASTToTargetAST.java
index b33f4ea4..541eb761 100644
--- a/src/main/java/de/dhbwstuttgart/target/generate/ASTToTargetAST.java
+++ b/src/main/java/de/dhbwstuttgart/target/generate/ASTToTargetAST.java
@@ -499,15 +499,17 @@ public class ASTToTargetAST {
 
             // For eliminating inner type variables we need to figure out which ones are actually used
             // TODO Maybe don't do this twice?
-            var referenced = new HashSet<TypePlaceholder>();
+            var usedTphs = new HashSet<TypePlaceholder>();
             for (var param : method.getParameterList().getFormalparalist()) {
-                referenced.addAll(findTypeVariables(param.getType()));
+                usedTphs.addAll(findTypeVariables(param.getType()));
             }
-            referenced.addAll(findTypeVariables(method.getReturnType()));
+            usedTphs.addAll(findTypeVariables(method.getReturnType()));
+            var referenced = new HashSet<>(usedTphs);
             referenced.addAll(typeVariablesOfClass);
 
             eliminateInnerTypeVariables(referenced, result);
-            usedTPHsOfMethods.put(method, referenced);
+
+            usedTPHsOfMethods.put(method, usedTphs);
 
             System.out.println(method.name + ": " + result);