diff --git a/src/libcharon/plugins/xauth_pam/xauth_pam_listener.c b/src/libcharon/plugins/xauth_pam/xauth_pam_listener.c
index eb06f54bb..5b77b99e2 100644
--- a/src/libcharon/plugins/xauth_pam/xauth_pam_listener.c
+++ b/src/libcharon/plugins/xauth_pam/xauth_pam_listener.c
@@ -65,7 +65,8 @@ static int conv(int num_msg, const struct pam_message **msg,
 			return PAM_CONV_ERR;
 		}
 	}
-	return PAM_SUCCESS;
+	*resp = calloc(num_msg, sizeof(struct pam_response));
+	return (*resp || !num_msg) ? PAM_SUCCESS : PAM_BUF_ERR;
 }
 
 METHOD(listener_t, ike_updown, bool,