diff --git a/automated/build.sh b/automated/build.sh
index 2d5d11ef..9bc055a8 100755
--- a/automated/build.sh
+++ b/automated/build.sh
@@ -20,7 +20,7 @@ if [ $SHORTNAME = "lts" ]
 then
     TAG=$(echo $TARGET | sed 's@^lts-\([0-9]*\)\.[0-9]*@lts\1@')
     WORKDIR=$ROOT/work/$(echo $TARGET | sed 's@^lts-\([0-9]*\)\.[0-9]*@lts-\1@')
-    if [ -n "$NOPLAN" ]; then
+    if [ -n "${NOPLAN:-}" ]; then
         echo '* DO NOT EDIT work/ files: commit to lts-haskell/build-constraints! *'
         exit 1
     fi