diff --git a/.travis.yml b/.travis.yml
index dcd562d..2ef035b 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -1,4 +1,8 @@
 language: rust
+rust:
+  - 1.21.0
+  - stable
+  - nightly
 sudo: false
 script:
   - cargo build --verbose
diff --git a/README.md b/README.md
index 51b9e08..28084a9 100644
--- a/README.md
+++ b/README.md
@@ -6,6 +6,8 @@ as described in
 
 [Documentation](https://unicode-rs.github.io/unicode-normalization/unicode_normalization/index.html)
 
+This crate requires Rust 1.21+.
+
 ```rust
 extern crate unicode_normalization;