diff --git a/RELEASE_NOTES.md b/RELEASE_NOTES.md
index 9ea997d..3d5daf2 100644
--- a/RELEASE_NOTES.md
+++ b/RELEASE_NOTES.md
@@ -1,3 +1,6 @@
+### 1.2.22
+- fixed exception in ASet.ofSetTree/ofListTree
+
 ### 1.2.21
 - fixed ASet.ofSetTree/ofListTree: ignore nested dirty updates
 
diff --git a/src/FSharp.Data.Adaptive/CollectionExtensions.fs b/src/FSharp.Data.Adaptive/CollectionExtensions.fs
index 117fe4f..3696e4e 100644
--- a/src/FSharp.Data.Adaptive/CollectionExtensions.fs
+++ b/src/FSharp.Data.Adaptive/CollectionExtensions.fs
@@ -324,8 +324,8 @@ module CollectionExtensions =
                     //  -> prevent updates to be included in delta computation
                     if subReader.OutOfDate then
                         removedDirty.Add(subReader) |> ignore
-                    elif not (subReader.Outputs.Remove x) then
-                        unexpected()
+                    else 
+                        subReader.Outputs.Remove x |> ignore // possible that we are not registered as output?
 
                     delta <- delta.Add (Rem n)
                     subReader.State |> IndexList.iteri (fun i old ->
@@ -397,8 +397,8 @@ module CollectionExtensions =
                         //  -> prevent updates to be included in delta computation
                         if subReader.OutOfDate then
                             removedDirty.Add(subReader) |> ignore
-                        elif not (subReader.Outputs.Remove x) then
-                            unexpected()
+                        else
+                            subReader.Outputs.Remove x |> ignore // possible that we are not registred as output?
 
                         delta <- delta.Add (Rem n)
                         for old in subReader.State do