diff --git a/.travis.yml b/.travis.yml
index 964c050c74..389d09830f 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -20,10 +20,9 @@ branches:
 install:
   - sudo curl -L https://nixos.org/nix/install | sh
   - . $HOME/.nix-profile/etc/profile.d/nix.sh
-  - nix-shell
 
 script:
-  - HYPOTHESIS_PROFILE=travis-ci pytest -v -k dataflow
+  - nix-shell --run 'HYPOTHESIS_PROFILE=travis-ci pytest -v -k dataflow'
 
 # CACHING. See https://nixos.wiki/wiki/Nix_on_Travis