diff --git a/vignettes/intro-to-interface.Rmd b/vignettes/intro-to-interface.Rmd
index 08e7144..aa20af4 100644
--- a/vignettes/intro-to-interface.Rmd
+++ b/vignettes/intro-to-interface.Rmd
@@ -255,7 +255,7 @@ Define functions with strict type constraints:
 typed_fun <- fun(
     x = numeric,
     y = numeric,
-    return = numeric,
+    return_type = numeric,
     impl = function(x, y) {
         return(x + y)
     }
@@ -288,6 +288,8 @@ print(typed_fun2(1, 2))  # [1] 3
 print(typed_fun2("a", 2))  # [1] "a 2"
 ```
 
+<!-- TODO: custom return functions for typed fun and enums -->
+
 ### Typed `data.frame`/`data.table`s
 
 Create data frames with column type constraints and row validation: