diff --git a/src/lib-storage/mail-storage-service.c b/src/lib-storage/mail-storage-service.c
index ddc412591d..8aa86f3698 100644
--- a/src/lib-storage/mail-storage-service.c
+++ b/src/lib-storage/mail-storage-service.c
@@ -324,6 +324,7 @@ service_auth_userdb_lookup(struct mail_storage_service_ctx *ctx,
 	info.remote_ip = input->remote_ip;
 	info.local_port = input->local_port;
 	info.remote_port = input->remote_port;
+	info.debug = input->debug;
 
 	ret = auth_master_user_lookup(ctx->conn, *user, &info, pool,
 				      &new_username, fields_r);
diff --git a/src/lib-storage/mail-storage-service.h b/src/lib-storage/mail-storage-service.h
index 2baf9ba3e1..65b633194d 100644
--- a/src/lib-storage/mail-storage-service.h
+++ b/src/lib-storage/mail-storage-service.h
@@ -58,6 +58,8 @@ struct mail_storage_service_input {
 
 	/* override MAIL_STORAGE_SERVICE_FLAG_USERDB_LOOKUP for this lookup */
 	unsigned int no_userdb_lookup:1;
+	/* Enable auth_debug=yes for this lookup */
+	unsigned int debug:1;
 };
 
 extern struct module *mail_storage_service_modules;