diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
index 21b04c3eda41..001f74fc0ce5 100644
--- a/drivers/gpu/drm/i915/intel_dp.c
+++ b/drivers/gpu/drm/i915/intel_dp.c
@@ -1041,10 +1041,10 @@ intel_dp_aux_transfer(struct drm_dp_aux *aux, struct drm_dp_aux_msg *msg)
 		if (WARN_ON(txsize > 20))
 			return -E2BIG;
 
+		WARN_ON(!msg->buffer != !msg->size);
+
 		if (msg->buffer)
 			memcpy(txbuf + HEADER_SIZE, msg->buffer, msg->size);
-		else
-			WARN_ON(msg->size);
 
 		ret = intel_dp_aux_ch(intel_dp, txbuf, txsize, rxbuf, rxsize);
 		if (ret > 0) {