diff --git a/powa/dashboards.py b/powa/dashboards.py
index 7736f9f3..1a7e6c77 100644
--- a/powa/dashboards.py
+++ b/powa/dashboards.py
@@ -152,7 +152,7 @@ def notify_allowed(self):
         try:
             cur.execute(
                 """WITH s(v) AS (
-                    SELECT unnest(%s)
+                    SELECT unnest(%s::text[])
                     UNION ALL
                     SELECT rolname
                     FROM {powa}.powa_roles