diff --git a/script/cibuild b/script/cibuild
index 9a6675f7..7103653b 100755
--- a/script/cibuild
+++ b/script/cibuild
@@ -8,7 +8,7 @@ args=$@
 branch=$TRAVIS_BRANCH
 
 # the presence of $TRAVIS_PULL_REQUEST tells us whether this is a pull request
-if [[ "$TRAVIS_PULL_REQUEST" != "" ]]; then
+if [[ "$TRAVIS_PULL_REQUEST" != "false" ]]; then
   target_branch=$TRAVIS_PULL_REQUEST_BRANCH
   # if the *source* branch begins with "release"
   if [[ "$branch" =~ ^release ]]; then