diff --git a/README.md b/README.md
index 7273ff9..88d3ddd 100644
--- a/README.md
+++ b/README.md
@@ -12,7 +12,9 @@ Cross-origin resource sharing (CORS) for [Rocket](https://rocket.rs/) applicatio
 ## Requirements
 
 - Nightly Rust
-- Rocket >= 0.3
+- Rocket >= 0.4
+
+If you are using Rocket 0.3, use the `0.3.0` version of this crate.
 
 ### Nightly Rust
 
diff --git a/src/lib.rs b/src/lib.rs
index 57f022b..4d56907 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -10,7 +10,9 @@
 //! ## Requirements
 //!
 //! - Nightly Rust
-//! - Rocket >= 0.3
+//! - Rocket >= 0.4
+//!
+//! If you are using Rocket 0.3, use the `0.3.0` version of this crate.
 //!
 //! ### Nightly Rust
 //!