diff --git a/.travis.yml b/.travis.yml
index 70aa27f..0149fad 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -14,7 +14,7 @@ jobs:
     script: make check
   - stage: Build Docker Containers
     name: Build Heroku 18
-    script: docker build --pull --tag heroku-python-build-heroku-18 --file $(shell pwd)/Dockerfile.heroku-18 .
+    script: docker build --pull --tag heroku-python-build-heroku-18 --file $(pwd)/Dockerfile.heroku-18 .
   - stage: Test Runs
     script: docker run --rm heroku-python-build-heroku-18 bash test/run-deps
     script: docker run --rm heroku-python-build-heroku-18 bash test/run-versions