diff --git a/core/src/main/scala/stainless/verification/TypeChecker.scala b/core/src/main/scala/stainless/verification/TypeChecker.scala
index 10649fdc2..34eea759f 100644
--- a/core/src/main/scala/stainless/verification/TypeChecker.scala
+++ b/core/src/main/scala/stainless/verification/TypeChecker.scala
@@ -152,7 +152,7 @@ class TypeChecker(val program: StainlessProgram, val context: inox.Context, val
   }
 
   case object SetEdge extends Edge {
-    def polarity(polarities: mutable.Map[(Identifier,Identifier),Polarity]) = Nothing
+    def polarity(polarities: mutable.Map[(Identifier,Identifier),Polarity]) = StrictlyPositive
   }
 
   case object BagEdge extends Edge {