diff --git a/src/Fable.Transforms/Replacements.fs b/src/Fable.Transforms/Replacements.fs
index ae22db94b1..f3ac4c94e5 100644
--- a/src/Fable.Transforms/Replacements.fs
+++ b/src/Fable.Transforms/Replacements.fs
@@ -717,6 +717,8 @@ let identityHash r (arg: Expr) =
         Helper.CoreCall("Util", "structuralHash", Number Int32, [arg], ?loc=r)
     | DeclaredType(ent,_) when ent.IsFSharpUnion || ent.IsFSharpRecord || ent.IsValueType ->
         Helper.CoreCall("Util", "structuralHash", Number Int32, [arg], ?loc=r)
+    | DeclaredType(ent,_) ->
+        Helper.InstanceCall(arg, "GetHashCode", Number Int32, [], ?loc=r)
     | _ ->
         Helper.CoreCall("Util", "identityHash", Number Int32, [arg], ?loc=r)
 
diff --git a/src/fable-library/List.fs b/src/fable-library/List.fs
index dd1df15954..2997eba6b4 100644
--- a/src/fable-library/List.fs
+++ b/src/fable-library/List.fs
@@ -8,58 +8,72 @@ open Fable.Core
 let msgListWasEmpty = "List was empty"
 let msgListNoMatch = "List did not contain any matching elements"
 
-[<CustomEquality; CustomComparison>]
-type List<'T> when 'T : comparison =
-    { Count: int; Values: ResizeArray<'T> }
+type List<'T when 'T: comparison>(Count: int, Values: ResizeArray<'T>) =
+    let mutable hashCode = None
 
-    static member Empty =
-        { Count = 0; Values = ResizeArray<'T>() }
-    static member Cons (x: 'T, xs: 'T list) =
+    static member Empty = new List<'T>(0, ResizeArray<'T>())
+    static member Cons (x: 'T, xs: 'T list) = xs.Add(x)
+
+    member _.Add(x: 'T) =
         let values =
-            if xs.Count = xs.Values.Count
-            then xs.Values
-            else xs.Values.GetRange(0, xs.Count)
+            if Count = Values.Count
+            then Values
+            else Values.GetRange(0, Count)
         values.Add(x)
-        { Count = values.Count; Values = values }
+        new List<'T>(values.Count, values)
+
+    member _.IsEmpty = Count <= 0
+    member _.Length = Count
+
+    member _.Head =
+        if Count > 0
+        then Values.[Count - 1]
+        else failwith msgListWasEmpty
+
+    member _.Tail =
+        if Count > 0
+        then new List<'T>(Count - 1, Values)
+        else failwith msgListWasEmpty
+
+    member _.Item with get(index) =
+        Values.[Count - 1 - index]
 
     override xs.ToString() =
         "[" + System.String.Join("; ", xs) + "]"
 
-    override xs.GetHashCode() =
-        let inline combineHash x y = (x <<< 1) + y + 631
-        let mutable res = 0
-        for i = xs.Count - 1 downto 0 do
-            res <- combineHash res (hash xs.Values.[i])
-        res
+    override xs.Equals(other: obj) =
+        let ys = other :?> 'T list
+        if xs.Length <> ys.Length then false
+        elif xs.GetHashCode() <> ys.GetHashCode() then false
+        else Seq.forall2 (Unchecked.equals) xs ys
+        // (xs :> System.IComparable).CompareTo(other) = 0
 
-    override xs.Equals(that: obj) =
-        (xs :> System.IComparable).CompareTo(that) = 0
+    override xs.GetHashCode() =
+        match hashCode with
+        | Some h -> h
+        | None ->
+            let inline combineHash i x y = (x <<< 1) + y + 631 * i
+            let len = min (xs.Length - 1) 18 // limit the hash count
+            let mutable h = 0
+            for i = 0 to len do
+                h <- combineHash i h (hash xs.[i])
+            hashCode <- Some h
+            h
 
     interface System.IComparable with
-        member xs.CompareTo(that: obj) =
-            List.CompareWith compare xs (that :?> 'T list)
+        member xs.CompareTo(other: obj) =
+            List.CompareWith compare xs (other :?> 'T list)
 
     interface System.Collections.Generic.IEnumerable<'T> with
         member xs.GetEnumerator(): System.Collections.Generic.IEnumerator<'T> =
-            let elems = seq { for i = xs.Count - 1 downto 0 do yield xs.Values.[i] }
+            let len = xs.Length - 1
+            let elems = seq { for i = 0 to len do yield xs.[i] }
             elems.GetEnumerator()
+
     interface System.Collections.IEnumerable with
         member this.GetEnumerator(): System.Collections.IEnumerator =
             ((this :> System.Collections.Generic.IEnumerable<'T>).GetEnumerator() :> System.Collections.IEnumerator)
 
-    member xs.Length = xs.Count
-    member xs.Head =
-        if xs.Count > 0
-        then xs.Values.[xs.Count - 1]
-        else failwith msgListWasEmpty
-    member xs.Tail =
-        if xs.Count > 0
-        then { Count = xs.Count - 1; Values = xs.Values }
-        else failwith msgListWasEmpty
-    member xs.IsEmpty = xs.Count <= 0
-    member xs.Item with get(index) =
-        xs.Values.[xs.Count - 1 - index]
-
     static member CompareWith (comparer: 'T -> 'T -> int) (xs: 'T list) (ys: 'T list): int =
         if obj.ReferenceEquals(xs, ys)
         then 0
@@ -80,9 +94,7 @@ type List<'T> when 'T : comparison =
 
 and 'T list when 'T: comparison = List<'T>
 
-open System.Collections.Generic
-
-let newList (values: ResizeArray<'T>) = { Count = values.Count; Values = values }
+let newList (values: ResizeArray<'T>) = new List<'T>(values.Count, values)
 
 let empty () = List.Empty
 
@@ -213,7 +225,7 @@ let iterateIndexed f xs =
 let iterateIndexed2 f xs ys =
     fold2 (fun i x y -> f i x y; i + 1) 0 xs ys |> ignore
 
-let ofArray (xs: IList<'T>) =
+let ofArray (xs: System.Collections.Generic.IList<'T>) =
     let mutable res = List.Empty
     for i = xs.Count - 1 downto 0 do
         res <- cons xs.[i] res
@@ -315,13 +327,13 @@ let choose f xs =
         | Some y -> cons y acc
         | None -> acc) List.Empty xs |> reverse
 
-let contains (value: 'T) (xs: 'T list) ([<Inject>] eq: IEqualityComparer<'T>) =
+let contains (value: 'T) (xs: 'T list) ([<Inject>] eq: System.Collections.Generic.IEqualityComparer<'T>) =
     tryFindIndex (fun v -> eq.Equals (value, v)) xs |> Option.isSome
 
-let except (itemsToExclude: seq<'t>) (xs: 't list) ([<Inject>] eq: IEqualityComparer<'t>): 't list =
+let except (itemsToExclude: seq<'t>) (xs: 't list) ([<Inject>] eq: System.Collections.Generic.IEqualityComparer<'t>): 't list =
     if isEmpty xs then xs
     else
-        let cached = HashSet(itemsToExclude, eq)
+        let cached = System.Collections.Generic.HashSet(itemsToExclude, eq)
         xs |> filter cached.Add
 
 let initialize n f =
@@ -373,16 +385,16 @@ let sortWith (comparison: 'T -> 'T -> int) (xs: 'T list): 'T list =
     values.Sort(System.Comparison<_>(comparison))
     values |> ofSeq
 
-let sort (xs: 'T list) ([<Inject>] comparer: IComparer<'T>): 'T list =
+let sort (xs: 'T list) ([<Inject>] comparer: System.Collections.Generic.IComparer<'T>): 'T list =
     sortWith (fun x y -> comparer.Compare(x, y)) xs
 
-let sortBy (projection: 'a -> 'b) (xs: 'a list) ([<Inject>] comparer: IComparer<'b>): 'a list =
+let sortBy (projection: 'a -> 'b) (xs: 'a list) ([<Inject>] comparer: System.Collections.Generic.IComparer<'b>): 'a list =
     sortWith (fun x y -> comparer.Compare(projection x, projection y)) xs
 
-let sortDescending (xs: 'T list) ([<Inject>] comparer: IComparer<'T>): 'T list =
+let sortDescending (xs: 'T list) ([<Inject>] comparer: System.Collections.Generic.IComparer<'T>): 'T list =
     sortWith (fun x y -> comparer.Compare(x, y) * -1) xs
 
-let sortByDescending (projection: 'a -> 'b) (xs: 'a list) ([<Inject>] comparer: IComparer<'b>): 'a list =
+let sortByDescending (projection: 'a -> 'b) (xs: 'a list) ([<Inject>] comparer: System.Collections.Generic.IComparer<'b>): 'a list =
     sortWith (fun x y -> comparer.Compare(projection x, projection y) * -1) xs
 
 let sum (xs: 'T list) ([<Inject>] adder: IGenericAdder<'T>): 'T =
@@ -391,16 +403,16 @@ let sum (xs: 'T list) ([<Inject>] adder: IGenericAdder<'T>): 'T =
 let sumBy (f: 'T -> 'T2) (xs: 'T list) ([<Inject>] adder: IGenericAdder<'T2>): 'T2 =
     fold (fun acc x -> adder.Add(acc, f x)) (adder.GetZero()) xs
 
-let maxBy (projection: 'a -> 'b) (xs: 'a list) ([<Inject>] comparer: IComparer<'b>): 'a =
+let maxBy (projection: 'a -> 'b) (xs: 'a list) ([<Inject>] comparer: System.Collections.Generic.IComparer<'b>): 'a =
     reduce (fun x y -> if comparer.Compare(projection y, projection x) > 0 then y else x) xs
 
-let max (li:'a list) ([<Inject>] comparer: IComparer<'a>): 'a =
+let max (li:'a list) ([<Inject>] comparer: System.Collections.Generic.IComparer<'a>): 'a =
     reduce (fun x y -> if comparer.Compare(y, x) > 0 then y else x) li
 
-let minBy (projection: 'a -> 'b) (xs: 'a list) ([<Inject>] comparer: IComparer<'b>): 'a =
+let minBy (projection: 'a -> 'b) (xs: 'a list) ([<Inject>] comparer: System.Collections.Generic.IComparer<'b>): 'a =
     reduce (fun x y -> if comparer.Compare(projection y, projection x) > 0 then x else y) xs
 
-let min (xs: 'a list) ([<Inject>] comparer: IComparer<'a>): 'a =
+let min (xs: 'a list) ([<Inject>] comparer: System.Collections.Generic.IComparer<'a>): 'a =
     reduce (fun x y -> if comparer.Compare(y, x) > 0 then x else y) xs
 
 let average (xs: 'T list) ([<Inject>] averager: IGenericAverager<'T>): 'T =
@@ -452,11 +464,11 @@ let splitAt i (xs: 'T list) =
     if i > xs.Length then invalidArg "index" "The input sequence has an insufficient number of elements."
     take i xs, skip i xs
 
-let distinctBy (projection: 'T -> 'Key) (xs: 'T list) ([<Inject>] eq: IEqualityComparer<'Key>) =
-    let hashSet = HashSet<'Key>(eq)
+let distinctBy (projection: 'T -> 'Key) (xs: 'T list) ([<Inject>] eq: System.Collections.Generic.IEqualityComparer<'Key>) =
+    let hashSet = System.Collections.Generic.HashSet<'Key>(eq)
     xs |> filter (projection >> hashSet.Add)
 
-let distinct (xs: 'T list) ([<Inject>] eq: IEqualityComparer<'T>) =
+let distinct (xs: 'T list) ([<Inject>] eq: System.Collections.Generic.IEqualityComparer<'T>) =
     distinctBy id xs eq
 
 let exactlyOne (xs: 'T list) =
@@ -465,8 +477,8 @@ let exactlyOne (xs: 'T list) =
     | 0 -> invalidArg "list" LanguagePrimitives.ErrorStrings.InputSequenceEmptyString
     | _ -> invalidArg "list" "Input list too long"
 
-let groupBy (projection: 'T -> 'Key) (xs: 'T list)([<Inject>] eq: IEqualityComparer<'Key>): ('Key * 'T list) list =
-    let dict = Dictionary<'Key, 'T list>(eq)
+let groupBy (projection: 'T -> 'Key) (xs: 'T list)([<Inject>] eq: System.Collections.Generic.IEqualityComparer<'Key>): ('Key * 'T list) list =
+    let dict = System.Collections.Generic.Dictionary<'Key, 'T list>(eq)
     let mutable keys = List.Empty
     xs |> iterate (fun v ->
         let key = projection v
@@ -480,8 +492,8 @@ let groupBy (projection: 'T -> 'Key) (xs: 'T list)([<Inject>] eq: IEqualityCompa
     keys |> iterate (fun key -> result <- cons (key, reverse dict.[key]) result)
     result
 
-let countBy (projection: 'T -> 'Key) (xs: 'T list)([<Inject>] eq: IEqualityComparer<'Key>) =
-    let dict = Dictionary<'Key, int>(eq)
+let countBy (projection: 'T -> 'Key) (xs: 'T list)([<Inject>] eq: System.Collections.Generic.IEqualityComparer<'Key>) =
+    let dict = System.Collections.Generic.Dictionary<'Key, int>(eq)
     let mutable keys = List.Empty
     xs |> iterate (fun v ->
         let key = projection v
diff --git a/tests/Main/ComparisonTests.fs b/tests/Main/ComparisonTests.fs
index a9d1b23fd2..190858f800 100644
--- a/tests/Main/ComparisonTests.fs
+++ b/tests/Main/ComparisonTests.fs
@@ -434,6 +434,10 @@ let tests =
         (OTest(1).GetHashCode(), OTest(1).GetHashCode()) ||> notEqual
         (OTest(2).GetHashCode(), OTest(1).GetHashCode()) ||> notEqual
 
+    testCase "GetHashCode with objects that overwrite it works" <| fun () ->
+        (Test(1).GetHashCode(), Test(1).GetHashCode()) ||> equal
+        (Test(2).GetHashCode(), Test(1).GetHashCode()) ||> notEqual
+
     testCase "GetHashCode with same object works" <| fun () ->
         let o = OTest(1)
         let h1 = o.GetHashCode()