diff --git a/.travis.yml b/.travis.yml
index 84aa6b0..68fbb3e 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -20,7 +20,6 @@ env:
     # Supply more than one RACKET_VERSION (as in the example below) to
     # create a Travis-CI build matrix to test against multiple Racket
     # versions.
-    - RACKET_VERSION=6.3
     - RACKET_VERSION=6.4
     - RACKET_VERSION=6.5
     - RACKET_VERSION=6.6