diff --git a/data/helpers.d/psql b/data/helpers.d/psql
index f960e6297..bdc9a07c2 100644
--- a/data/helpers.d/psql
+++ b/data/helpers.d/psql
@@ -141,7 +141,7 @@ ynh_psql_user_exists() {
 	# Manage arguments with getopts
 	ynh_handle_getopts_args "$@"
 
-	if [[ -z $(sudo --login --user=postgres PGUSER="postgres" PGPASSWORD="$(sudo cat $PSQL_ROOT_PWD_FILE)" psql -tAc "SELECT rolname FROM pg_roles WHERE rolname='$user';") ]]; then
+	if ! sudo --login --user=postgres PGUSER="postgres" PGPASSWORD="$(sudo cat $PSQL_ROOT_PWD_FILE)" psql -tAc "SELECT rolname FROM pg_roles WHERE rolname='$user';" | grep --quiet "$user" ; then
 		return 1
 	else
 		return 0
@@ -160,7 +160,7 @@ ynh_psql_database_exists() {
 	# Manage arguments with getopts
 	ynh_handle_getopts_args "$@"
 
-	if [[ -z $(sudo --login --user=postgres PGUSER="postgres" PGPASSWORD="$(sudo cat $PSQL_ROOT_PWD_FILE)" psql -tAc "SELECT datname FROM pg_database WHERE datname='$database';") ]]; then
+	if ! sudo --login --user=postgres PGUSER="postgres" PGPASSWORD="$(sudo cat $PSQL_ROOT_PWD_FILE)" psql -tAc "SELECT datname FROM pg_database WHERE datname='$database';" | grep --quiet "$user"; then
 		return 1
 	else
 		return 0