diff --git a/src/FsCheck/ReflectArbitrary.fs b/src/FsCheck/ReflectArbitrary.fs
index 6a87a6e5..8440d2ae 100644
--- a/src/FsCheck/ReflectArbitrary.fs
+++ b/src/FsCheck/ReflectArbitrary.fs
@@ -190,9 +190,9 @@ module internal ReflectArbitrary =
                 if Seq.isEmpty children then 0 
                 elif Seq.exists ((=) t) children then 2 
                 else 1
-            let info,_ = FSharpValue.GetUnionFields(o,t)
-            let makeCase = FSharpValue.PreComputeUnionConstructor info
-            let readCase = FSharpValue.PreComputeUnionReader info
+            let info,_ = FSharpValue.GetUnionFields(o,t,true)
+            let makeCase = FSharpValue.PreComputeUnionConstructor(info,true)
+            let readCase = FSharpValue.PreComputeUnionReader(info,true)
             let childrenTypes = info.GetFields() |> Array.map ( fun x -> x.PropertyType )
             let partitionCase t s0 (_,(_,children,make,_)) =
                 match unionSize t children with
diff --git a/tests/FsCheck.Test/Arbitrary.fs b/tests/FsCheck.Test/Arbitrary.fs
index 83bba1df..bd5f6609 100644
--- a/tests/FsCheck.Test/Arbitrary.fs
+++ b/tests/FsCheck.Test/Arbitrary.fs
@@ -692,12 +692,20 @@ module Arbitrary =
     let ``Derive generator for private two value record``() =
         generate<PrivateRecord> |> sample 10 |> ignore
 
+    [<Property>]
+    let ``Shrink for private two value record`` (DoNotShrink (value: PrivateRecord)) =
+        shrink value |> ignore
+
     type PrivateUnion = private | Case1 | Case2 of string
 
     [<Fact>]
     let ``Derive generator for private two case union``() =
         generate<PrivateUnion> |> sample 10 |> ignore
 
+    [<Property>]
+    let ``Shrink for private two case union`` (DoNotShrink (value: PrivateUnion)) =
+        shrink value |> ignore
+
     [<Fact>]
     let ``should not crash on isCSharpDto issue #545``() =
         try