2 files changed, 2 insertions, 2 deletions
diff --git a/sources/scala/collection/mutable/ObservableMap.scala b/sources/scala/collection/mutable/ObservableMap.scala
index 52de275828..40aeddca77 100644
--- a/sources/scala/collection/mutable/ObservableMap.scala
+++ b/sources/scala/collection/mutable/ObservableMap.scala
@@ -43,6 +43,6 @@ abstract class ObservableMap[A, B, This <: ObservableMap[A, B, This]]: This
 
     abstract override def clear: Unit = {
         super.clear;
-        publish(new Reset() with Undo { def undo = error("cannot undo"); });
+        publish(new Reset() with Undo { def undo: Unit = error("cannot undo"); });
     }
 }
diff --git a/sources/scala/collection/mutable/ObservableSet.scala b/sources/scala/collection/mutable/ObservableSet.scala
index e3ec93ad05..0bd4cef331 100644
--- a/sources/scala/collection/mutable/ObservableSet.scala
+++ b/sources/scala/collection/mutable/ObservableSet.scala
@@ -33,6 +33,6 @@ abstract class ObservableSet[A, This <: ObservableSet[A, This]]: This
 
     abstract override def clear: Unit = {
         super.clear;
-        publish(new Reset() with Undo { def undo = error("cannot undo"); });
+        publish(new Reset() with Undo { def undo: Unit = error("cannot undo"); });
     }
 }