diff --git a/src/fsharp/FSharp.Core/array.fs b/src/fsharp/FSharp.Core/array.fs
index f9cced85d3b..b92e3d95034 100644
--- a/src/fsharp/FSharp.Core/array.fs
+++ b/src/fsharp/FSharp.Core/array.fs
@@ -405,10 +405,12 @@ namespace Microsoft.FSharp.Collections
             loop 0
 
         let inline groupByImpl (comparer:IEqualityComparer<'SafeKey>) (keyf:'T->'SafeKey) (getKey:'SafeKey->'Key) (array: 'T[]) =
+            let length = array.Length
+            if length = 0 then Microsoft.FSharp.Primitives.Basics.Array.zeroCreateUnchecked 0 else
             let dict = Dictionary<_,ResizeArray<_>> comparer
 
             // Build the groupings
-            for i = 0 to (array.Length - 1) do
+            for i = 0 to length - 1 do
                 let v = array.[i]
                 let safeKey = keyf v
                 let mutable prev = Unchecked.defaultof<_>
diff --git a/src/fsharp/FSharp.Core/local.fs b/src/fsharp/FSharp.Core/local.fs
index 779b543cd21..42297795184 100644
--- a/src/fsharp/FSharp.Core/local.fs
+++ b/src/fsharp/FSharp.Core/local.fs
@@ -196,6 +196,10 @@ module internal List =
                 cons
                   
     let groupBy (comparer:IEqualityComparer<'SafeKey>) (keyf:'T->'SafeKey) (getKey:'SafeKey->'Key) (list: 'T list) =
+        match list with
+        | [] -> []
+        | _ ->
+
         let dict = Dictionary<_, _ list []> comparer
 
         // Build the groupings
diff --git a/src/fsharp/FSharp.Core/seq.fs b/src/fsharp/FSharp.Core/seq.fs
index f057e8f3fd0..f8ef697a8e5 100644
--- a/src/fsharp/FSharp.Core/seq.fs
+++ b/src/fsharp/FSharp.Core/seq.fs
@@ -1032,6 +1032,8 @@ namespace Microsoft.FSharp.Collections
         let inline groupByImpl (comparer:IEqualityComparer<'SafeKey>) (keyf:'T->'SafeKey) (getKey:'SafeKey->'Key) (seq:seq<'T>) =
             checkNonNull "seq" seq
 
+            if isEmpty seq then empty else
+
             let dict = Dictionary<_,ResizeArray<_>> comparer
 
             // Previously this was 1, but I think this is rather stingy, considering that we are already paying