diff --git a/types/deep-freeze/deep-freeze-tests.ts b/types/deep-freeze/deep-freeze-tests.ts
index b8a6061859..d021944ff4 100644
--- a/types/deep-freeze/deep-freeze-tests.ts
+++ b/types/deep-freeze/deep-freeze-tests.ts
@@ -5,3 +5,6 @@ class Foo {
 }
 const foo = df(new Foo());
 const items = df([{id: 0, name: 'first'}]);
+const functionTest = df({id: 0, name: 'first', update: (blah: boolean) => blah});
+
+functionTest.update(true);
diff --git a/types/deep-freeze/index.d.ts b/types/deep-freeze/index.d.ts
index 16e183d185..ca8ceeca53 100644
--- a/types/deep-freeze/index.d.ts
+++ b/types/deep-freeze/index.d.ts
@@ -2,7 +2,7 @@
 // Project: https://github.com/substack/deep-freeze
 // Definitions by: Bart van der Schoor <https://github.com/Bartvds>, Aluan Haddad <https://github.com/aluanhaddad>
 // Definitions: https://github.com/DefinitelyTyped/DefinitelyTyped
-// TypeScript Version: 2.1
+// TypeScript Version: 3.1
 
 export = deepFreeze;
 
@@ -11,7 +11,8 @@ declare function deepFreeze<T extends Function>(f: T): T;
 declare function deepFreeze<T>(o: T): deepFreeze.DeepReadonly<T>;
 
 declare namespace deepFreeze {
-    type DeepReadonly<T> = {
-        readonly [P in keyof T]: DeepReadonly<T[P]>
-    };
+    type DeepReadonly<T> =
+        T extends (...args: any) => any
+            ? T
+            : { readonly [P in keyof T]: DeepReadonly<T[P]> };
 }