diff --git a/src/de/dhbwstuttgart/typeinference/unify/RuleSet.java b/src/de/dhbwstuttgart/typeinference/unify/RuleSet.java
index 0b51a25e..b3cb0dec 100644
--- a/src/de/dhbwstuttgart/typeinference/unify/RuleSet.java
+++ b/src/de/dhbwstuttgart/typeinference/unify/RuleSet.java
@@ -429,7 +429,9 @@ public class RuleSet implements IRuleSet{
 		Unifier unif = Unifier.identity();
 		for(int i = 0; i < typeDParams.size(); i++) { 
 			System.out.println("ADAPT" +typeDgenParams);
+			if (typeDgenParams.get(i) instanceof PlaceholderType) 
 			unif.add((PlaceholderType) typeDgenParams.get(i), typeDParams.get(i));
+			else System.out.println("ERROR");
 		}
 		return Optional.of(new UnifyPair(unif.apply(newLhs), typeDs, PairOperator.SMALLERDOT));
 	}