diff --git a/src/fsharp/FSharp.Core/string.fs b/src/fsharp/FSharp.Core/string.fs
index e620e4cac6a..df51fccd031 100644
--- a/src/fsharp/FSharp.Core/string.fs
+++ b/src/fsharp/FSharp.Core/string.fs
@@ -103,8 +103,4 @@ namespace Microsoft.FSharp.Core
                 check 0  
 
         [<CompiledName("Length")>]
-        let length (str:string) =
-            if String.IsNullOrEmpty str then
-                0
-            else
-                str.Length
+        let length (str:string) = if isNull str then 0 else str.Length