diff --git a/docs/user-defined-type-functions.md b/docs/user-defined-type-functions.md
index 3e7a047..464a9ba 100644
--- a/docs/user-defined-type-functions.md
+++ b/docs/user-defined-type-functions.md
@@ -104,7 +104,7 @@ All attributes of newly created typelib are initialized with empty tables / arra
 | `getintersection(arg: {typelib})` | `typelib` | returns an immutable runtime representation of intersection type of its argument |
 | `newtable(props: {[typelib]: typelib}, indexer: {key: typelib, value: typelib}?)` | `typelib` | returns a mutable runtime representation of a `table` type |
 | `newmetatable()` | `typelib` | returns a mutable runtime representation of a metatable represented as a special property of the `table` type |
-| `newfunction(parameters: {typelib} \| typelib)?, returns: {typelib} \| typelib)?)` | `typelib` | returns a mutable runtime representation of a `function` type. Calling `newfunction(X)` will by default set `parameters` to `X` |
+| `newfunction(parameters: {typelib} \| typelib?, returns: {typelib} \| typelib?)` | `typelib` | returns a mutable runtime representation of a `function` type. Calling `newfunction(X)` will by default set `parameters` to `X` |
 | `isnil(arg: typelib)` | `boolean` | returns true if the argument is syntactically a runtime representation of the built-in type `nil` |
 | `isunknown(arg: typelib)` | `boolean` | returns true if the argument is syntactically a runtime representation of the built-in type `unknown` |
 | `isnever(arg: typelib)` | `boolean` | returns true if the argument is syntactically a runtime representation of the built-in type `never` |