diff --git a/src/unsafe/unions.md b/src/unsafe/unions.md
index f0199756..02f03e0f 100644
--- a/src/unsafe/unions.md
+++ b/src/unsafe/unions.md
@@ -15,3 +15,14 @@ fn main() {
     println!("bool: {}", unsafe { u.b });  // Undefined behavior!
 }
 ```
+
+<details>
+
+Unions are very rarely needed in Rust as you can usually use an enum. They are occasionally needed
+for interacting with C library APIs.
+
+If you just want to reinterpret bytes as a different type, you probably want
+[`std::mem::transmute`](https://doc.rust-lang.org/stable/std/mem/fn.transmute.html) or a safe
+wrapper such as the [`zerocopy`](https://crates.io/crates/zerocopy) crate.
+
+</details>