diff --git a/install_mysql.sh b/install_mysql.sh
index 19d15e2..5c95c02 100755
--- a/install_mysql.sh
+++ b/install_mysql.sh
@@ -245,7 +245,7 @@ fi
 
 if [[ -n "$(which mysqld)" ]] ; then
 
-   if $PARALLEL_INSTALLATION && ! $UPDATE_MYSQL ; then
+   if ! $PARALLEL_INSTALLATION && ! $UPDATE_MYSQL ; then
       fatal "Found binary '$(which mysqld)', but you are not in update mode!"
    fi