diff --git a/hwmon/mailbox_proto.h b/hwmon/mailbox_proto.h
index ea81064..34e7bdb 100644
--- a/hwmon/mailbox_proto.h
+++ b/hwmon/mailbox_proto.h
@@ -356,7 +356,7 @@ struct xcl_mailbox_clock_freqscaling {
 struct xcl_mailbox_req {
 	uint64_t flags;
 	int32_t req;
-	int32_t data[1]; /* variable length of payload from now on */
+	int32_t *data; /* variable length of payload from now on */
 };
 
 /**