diff --git a/AlgebraicDataflowArchitectureModel/src/models/dataConstraintModel/DataConstraintModel.java b/AlgebraicDataflowArchitectureModel/src/models/dataConstraintModel/DataConstraintModel.java
index 335d392..08a2601 100644
--- a/AlgebraicDataflowArchitectureModel/src/models/dataConstraintModel/DataConstraintModel.java
+++ b/AlgebraicDataflowArchitectureModel/src/models/dataConstraintModel/DataConstraintModel.java
@@ -177,7 +177,7 @@
 		mod.setSignature(new Type[] {typeInt, null, null});
 		cons.setInverses(new Symbol[] {head, tail});
 		cons.setSignature(new Type[] {typeList, null, typeList});
-		append.setSignature(new Type[] {typeList, null, typeList});
+		append.setSignature(new Type[] {typeList, typeList, null});
 		head.setSignature(new Type[] {null, typeList});
 		tail.setSignature(new Type[] {typeList, typeList});
 		contains.setSignature(new Type[] {typeBoolean, typeList, null});