diff --git a/.travis.yml b/.travis.yml
index e0712e1e4..3e5e73d06 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -10,4 +10,4 @@ before_script:
 script:
   - ./format -c
   - nix-shell . -A install
-  - nix-shell tests -A run.all
+  - nix-shell --pure tests -A run.all