diff --git a/napi-derive-example/src/lib.rs b/napi-derive-example/src/lib.rs
index 39ca3fac..d5755677 100644
--- a/napi-derive-example/src/lib.rs
+++ b/napi-derive-example/src/lib.rs
@@ -23,7 +23,7 @@ fn test_throw<'a>(_ctx: CallContext) -> Result<Value<'a, Any>> {
   Err(Error::new(Status::GenericFailure))
 }
 
-#[js_function]
+#[js_function(1)]
 fn fibonacci<'env>(ctx: CallContext<'env>) -> Result<Value<'env, Number>> {
   let n = ctx.get::<Number>(0)?.try_into()?;
   ctx.env.create_int64(fibonacci_native(n))
diff --git a/napi-derive/README.md b/napi-derive/README.md
index f42959e5..e8be009b 100644
--- a/napi-derive/README.md
+++ b/napi-derive/README.md
@@ -9,7 +9,7 @@ extern crate napi_rs_derive;
 use napi_rs::{Result, Value, CallContext, Number};
 use std::convert::TryInto;
 
-#[js_function]
+#[js_function(1)]
 fn fibonacci<'env>(ctx: CallContext<'env>) -> Result<Value<'env, Number>> {
   let n = ctx.get::<Number>(0)?.try_into()?;
   ctx.env.create_int64(fibonacci_native(n))