diff --git a/README.md b/README.md
index 99ce9018..2b70b36d 100644
--- a/README.md
+++ b/README.md
@@ -316,7 +316,7 @@ Functions declared with `private` are hidden and cannot be called from Rust (see
 // Define functions in a script.
 let ast = engine.compile(true,
     r#"
-        // a function with two parameters: String and i64
+        // a function with two parameters: string and i64
         fn hello(x, y) {
             x.len + y
         }
diff --git a/tests/call_fn.rs b/tests/call_fn.rs
index 0bed8d7b..29f7abca 100644
--- a/tests/call_fn.rs
+++ b/tests/call_fn.rs
@@ -89,6 +89,14 @@ fn test_anonymous_fn() -> Result<(), Box<EvalAltResult>> {
 
     assert_eq!(calc_func(42, 123, 9)?, 1485);
 
+    let calc_func = Func::<(INT, String, INT), INT>::create_from_script(
+        Engine::new(),
+        "fn calc(x, y, z) { (x + len(y)) * z }",
+        "calc",
+    )?;
+
+    assert_eq!(calc_func(42, "hello".to_string(), 9)?, 423);
+
     let calc_func = Func::<(INT, INT, INT), INT>::create_from_script(
         Engine::new(),
         "private fn calc(x, y, z) { (x + y) * z }",