diff --git a/gitbook/validation/ce.md b/gitbook/validation/ce.md
index f524c108..dec86ec7 100644
--- a/gitbook/validation/ce.md
+++ b/gitbook/validation/ce.md
@@ -14,7 +14,7 @@ This CE can take advantage of the [and! operator](https://github.com/fsharp/fsla
 
 ```fsharp
 // string -> Result<int, string>
-let tryParseInt str =
+let tryParseInt (str: string) =
   match System.Int32.TryParse str with
   | true, x -> Ok x
   | false, _ ->