diff --git a/src/doc/trpl/closures.md b/src/doc/trpl/closures.md
index 5b49df92fe3..51a0bb69a7c 100644
--- a/src/doc/trpl/closures.md
+++ b/src/doc/trpl/closures.md
@@ -51,7 +51,7 @@ defined. The closure borrows any variables it uses, so this will error:
 
 ```{rust,ignore}
 fn main() {
-    let mut x = 5;
+    let mut x: i32 = 5;
 
     let printer = |&:| { println!("x is: {}", x); };