diff --git a/.travis.yml b/.travis.yml
index 695bc3ba..40ad8d86 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -23,7 +23,7 @@ jobs:
 # Check if there are any cached images, copy them to our "images" directory
         - if [ -n "$(ls -A imgcache/*.zip)" ]; then mkdir -p images && cp imgcache/*.zip images; fi
       script:
-        - if [[ -z ${TRAVIS_TAG} && ${TRAVIS_PULL_REQUEST} ]]; then
+        - if [[ -z ${TRAVIS_TAG} && "${TRAVIS_PULL_REQUEST}" != "false" ]]; then
             echo "Commit range is ${TRAVIS_COMMIT_RANGE}" &&
             if [ $(git diff --name-only ${TRAVIS_COMMIT_RANGE} | grep -v ^"docs/" | wc -l) -eq 0 ]; then
               echo " === Docs-only change; skipping build ===" &&