diff --git a/libavcodec/libx265.c b/libavcodec/libx265.c
index 90658d3d9e..9395120471 100644
--- a/libavcodec/libx265.c
+++ b/libavcodec/libx265.c
@@ -35,6 +35,7 @@
 #include "encode.h"
 #include "internal.h"
 #include "packet_internal.h"
+#include "sei.h"
 
 typedef struct libx265Context {
     const AVClass *class;
@@ -51,6 +52,9 @@ typedef struct libx265Context {
     char *profile;
     AVDictionary *x265_opts;
 
+    void *sei_data;
+    int sei_data_size;
+
     /**
      * If the encoder does not support ROI then warn the first time we
      * encounter a frame with ROI side data.
@@ -78,6 +82,7 @@ static av_cold int libx265_encode_close(AVCodecContext *avctx)
     libx265Context *ctx = avctx->priv_data;
 
     ctx->api->param_free(ctx->params);
+    av_freep(&ctx->sei_data);
 
     if (ctx->encoder)
         ctx->api->encoder_close(ctx->encoder);
@@ -489,6 +494,8 @@ static int libx265_encode_frame(AVCodecContext *avctx, AVPacket *pkt,
     ctx->api->picture_init(ctx->params, &x265pic);
 
     if (pic) {
+        x265_sei *sei = &x265pic.userSEI;
+        sei->numPayloads = 0;
         for (i = 0; i < 3; i++) {
            x265pic.planes[i] = pic->data[i];
            x265pic.stride[i] = pic->linesize[i];
@@ -516,6 +523,32 @@ static int libx265_encode_frame(AVCodecContext *avctx, AVPacket *pkt,
 
             memcpy(x265pic.userData, &pic->reordered_opaque, sizeof(pic->reordered_opaque));
         }
+
+        for (i = 0; i < pic->nb_side_data; i++) {
+            AVFrameSideData *side_data = pic->side_data[i];
+            void *tmp;
+            x265_sei_payload *sei_payload;
+
+            if (side_data->type != AV_FRAME_DATA_SEI_UNREGISTERED)
+                continue;
+
+            tmp = av_fast_realloc(ctx->sei_data,
+                                  &ctx->sei_data_size,
+                                  (sei->numPayloads + 1) * sizeof(*sei_payload));
+            if (!tmp) {
+                av_freep(&x265pic.userData);
+                av_freep(&x265pic.quantOffsets);
+                return AVERROR(ENOMEM);
+            }
+            ctx->sei_data = tmp;
+            sei->payloads = ctx->sei_data;
+            sei_payload = &sei->payloads[sei->numPayloads];
+            sei_payload->payload = side_data->data;
+            sei_payload->payloadSize = side_data->size;
+            /* Equal to libx265 USER_DATA_UNREGISTERED */
+            sei_payload->payloadType = SEI_TYPE_USER_DATA_UNREGISTERED;
+            sei->numPayloads++;
+        }
     }
 
     ret = ctx->api->encoder_encode(ctx->encoder, &nal, &nnal,