diff --git a/docs/migration_to_1.0.0.md b/docs/migration_to_1.0.0.md
index ba59eae49..247e605a7 100644
--- a/docs/migration_to_1.0.0.md
+++ b/docs/migration_to_1.0.0.md
@@ -222,7 +222,7 @@ struct Env {
     counter: Arc<RefCell<i32>>,
 }
 
-fn get_counter(env: &mut Env) -> i32 {
+fn get_counter(env: &Env) -> i32 {
     *env.counter.borrow()
 }
 
@@ -343,4 +343,4 @@ you'll be able to delegate most of the work to Wasmer:
 [memory-pointers]: https://docs.wasmer.io/integrations/examples/memory-pointers
 [host-functions]: https://docs.wasmer.io/integrations/examples/host-functions
 [errors]: https://docs.wasmer.io/integrations/examples/errors
-[exit-early]: https://docs.wasmer.io/integrations/examples/exit-early
\ No newline at end of file
+[exit-early]: https://docs.wasmer.io/integrations/examples/exit-early