diff --git a/src/fsharp/check.fs b/src/fsharp/check.fs
index b2aa261e4d3..02aece18860 100644
--- a/src/fsharp/check.fs
+++ b/src/fsharp/check.fs
@@ -1125,6 +1125,18 @@ let CheckTopBinding cenv env (TBind(v,e,_) as bind) =
             check false v.DisplayName
             check false v.CompiledName
 
+            // Check if an F# extension member clashes
+            if v.IsExtensionMember then 
+                tcref.ModuleOrNamespaceType.AllValsAndMembersByLogicalNameUncached.[v.LogicalName] |> List.iter (fun v2 -> 
+                    if v2.IsExtensionMember && not (valEq v v2) && v.CompiledName = v2.CompiledName then
+                        let minfo1 =  FSMeth(cenv.g, generalizedTyconRef tcref, mkLocalValRef v, Some 0UL)
+                        let minfo2 =  FSMeth(cenv.g, generalizedTyconRef tcref, mkLocalValRef v2, Some 0UL)
+                        if tyconRefEq cenv.g v.MemberApparentParent v2.MemberApparentParent && 
+                           MethInfosEquivByNameAndSig EraseAll true cenv.g cenv.amap v.Range minfo1 minfo2 then 
+                            errorR(Duplicate(kind,v.DisplayName,v.Range)))
+
+
+
             // Properties get 'get_X', only if there are no args
             // Properties get 'get_X'
             match v.ValReprInfo with 
diff --git a/tests/fsharp/typecheck/sigs/neg23.bsl b/tests/fsharp/typecheck/sigs/neg23.bsl
index f5460a6d7cd..1d21a9a9a41 100644
--- a/tests/fsharp/typecheck/sigs/neg23.bsl
+++ b/tests/fsharp/typecheck/sigs/neg23.bsl
@@ -38,3 +38,11 @@ neg23.fs(92,18,92,21): typecheck error FS0439: The method 'X04' has curried argu
 neg23.fs(110,21,110,22): typecheck error FS0439: The method 'F' has curried arguments but has the same name as another method in this type. Methods with curried arguments cannot be overloaded. Consider using a method taking tupled arguments.
 
 neg23.fs(113,21,113,22): typecheck error FS0439: The method 'F' has curried arguments but has the same name as another method in this type. Methods with curried arguments cannot be overloaded. Consider using a method taking tupled arguments.
+
+neg23.fs(164,18,164,29): typecheck error FS0037: Two members called 'GroupRowsBy' have the same signature
+
+neg23.fs(165,18,165,29): typecheck error FS0037: Two members called 'GroupRowsBy' have the same signature
+
+neg23.fs(168,17,168,20): typecheck error FS0037: Two members called 'Foo' have the same signature
+
+neg23.fs(169,17,169,20): typecheck error FS0037: Two members called 'Foo' have the same signature
diff --git a/tests/fsharp/typecheck/sigs/neg23.fs b/tests/fsharp/typecheck/sigs/neg23.fs
index 24cf167bd34..cef3a34ae93 100644
--- a/tests/fsharp/typecheck/sigs/neg23.fs
+++ b/tests/fsharp/typecheck/sigs/neg23.fs
@@ -155,3 +155,15 @@ module PositiveTests =
         let y2 : int -> int = c.M2 (3,4)
         let y3 : int * int -> int -> int = c.M2
 
+
+type Frame = 
+  class 
+  end
+module X =
+  type Frame with
+    member frame.GroupRowsBy(key) = ()
+    member frame.GroupRowsBy(key) = ()
+    
+    // Up to erasure
+    member this.Foo (x:int->int) = printfn "method 1"
+    member this.Foo (x:FSharpFunc<int,int>) = printfn "method 2"