diff --git a/drivers/gpu/drm/vc4/vc4_hdmi.c b/drivers/gpu/drm/vc4/vc4_hdmi.c
index 94be67aa9ee5..184e1f0936c0 100644
--- a/drivers/gpu/drm/vc4/vc4_hdmi.c
+++ b/drivers/gpu/drm/vc4/vc4_hdmi.c
@@ -1444,13 +1444,20 @@ static irqreturn_t vc4_cec_irq_handler_thread(int irq, void *priv)
 
 static void vc4_cec_read_msg(struct vc4_hdmi *vc4_hdmi, u32 cntrl1)
 {
+	struct drm_device *dev = vc4_hdmi->connector.dev;
 	struct cec_msg *msg = &vc4_hdmi->cec_rx_msg;
 	unsigned int i;
 
 	msg->len = 1 + ((cntrl1 & VC4_HDMI_CEC_REC_WRD_CNT_MASK) >>
 					VC4_HDMI_CEC_REC_WRD_CNT_SHIFT);
+
+	if (msg->len > 16) {
+		drm_err(dev, "Attempting to read too much data (%d)\n", msg->len);
+		return;
+	}
+
 	for (i = 0; i < msg->len; i += 4) {
-		u32 val = HDMI_READ(HDMI_CEC_RX_DATA_1 + i);
+		u32 val = HDMI_READ(HDMI_CEC_RX_DATA_1 + (i >> 2));
 
 		msg->msg[i] = val & 0xff;
 		msg->msg[i + 1] = (val >> 8) & 0xff;
@@ -1543,11 +1550,17 @@ static int vc4_hdmi_cec_adap_transmit(struct cec_adapter *adap, u8 attempts,
 				      u32 signal_free_time, struct cec_msg *msg)
 {
 	struct vc4_hdmi *vc4_hdmi = cec_get_drvdata(adap);
+	struct drm_device *dev = vc4_hdmi->connector.dev;
 	u32 val;
 	unsigned int i;
 
+	if (msg->len > 16) {
+		drm_err(dev, "Attempting to transmit too much data (%d)\n", msg->len);
+		return -ENOMEM;
+	}
+
 	for (i = 0; i < msg->len; i += 4)
-		HDMI_WRITE(HDMI_CEC_TX_DATA_1 + i,
+		HDMI_WRITE(HDMI_CEC_TX_DATA_1 + (i >> 2),
 			   (msg->msg[i]) |
 			   (msg->msg[i + 1] << 8) |
 			   (msg->msg[i + 2] << 16) |