diff --git a/scripts/docker-library-build.sh b/scripts/docker-library-build.sh
index 43f4cc45..c1a45882 100755
--- a/scripts/docker-library-build.sh
+++ b/scripts/docker-library-build.sh
@@ -39,7 +39,7 @@ if [[ $branch =~ ^preview ]]; then
 else
   container_tag=$master_branch
 fi
-if [ -d "mariadb-docker/$master_branch" ]; then
+if [ ! -d "mariadb-docker/$master_branch" ]; then
   branch=main
 fi
 # Container tags must be lower case.