diff --git a/src/libstd/ffi/os_str.rs b/src/libstd/ffi/os_str.rs
index 1f384cbada3d..fbdb577a7f06 100644
--- a/src/libstd/ffi/os_str.rs
+++ b/src/libstd/ffi/os_str.rs
@@ -191,7 +191,7 @@ impl OsString {
     /// ```
     /// use std::ffi::OsString;
     ///
-    /// let mut os_string = OsString::with_capacity(10);
+    /// let os_string = OsString::with_capacity(10);
     /// let capacity = os_string.capacity();
     ///
     /// // This push is done without reallocating