diff --git a/modules/video_coding/codecs/vp9/test/vp9_impl_unittest.cc b/modules/video_coding/codecs/vp9/test/vp9_impl_unittest.cc
index 5b5db88b6e..f6594c1f7c 100644
--- a/modules/video_coding/codecs/vp9/test/vp9_impl_unittest.cc
+++ b/modules/video_coding/codecs/vp9/test/vp9_impl_unittest.cc
@@ -67,7 +67,14 @@ class TestVp9Impl : public VideoCodecUnitTest {
         EXPECT_EQ(vp9.temporal_idx, temporal_idx);
       }
       EXPECT_EQ(vp9.temporal_up_switch, temporal_up_switch);
-      EXPECT_EQ(vp9.num_ref_pics, num_ref_pics);
+
+      // Ensure there are no duplicates in reference list.
+      std::vector<uint8_t> vp9_p_diff(vp9.p_diff,
+                                      vp9.p_diff + vp9.num_ref_pics);
+      std::sort(vp9_p_diff.begin(), vp9_p_diff.end());
+      EXPECT_EQ(std::unique(vp9_p_diff.begin(), vp9_p_diff.end()),
+                vp9_p_diff.end());
+
       for (size_t ref_pic_num = 0; ref_pic_num < num_ref_pics; ++ref_pic_num) {
         EXPECT_NE(
             std::find(p_diff.begin(), p_diff.end(), vp9.p_diff[ref_pic_num]),
diff --git a/modules/video_coding/codecs/vp9/vp9_impl.cc b/modules/video_coding/codecs/vp9/vp9_impl.cc
index 5829bc1bf7..b4c13f9ccf 100644
--- a/modules/video_coding/codecs/vp9/vp9_impl.cc
+++ b/modules/video_coding/codecs/vp9/vp9_impl.cc
@@ -870,21 +870,30 @@ void VP9EncoderImpl::FillReferenceIndices(const vpx_codec_cx_pkt& pkt,
       const size_t fb_idx =
           enc_layer_conf.lst_fb_idx[layer_id.spatial_layer_id];
       RTC_DCHECK(ref_buf_.find(fb_idx) != ref_buf_.end());
-      ref_buf_list.push_back(ref_buf_.at(fb_idx));
+      if (std::find(ref_buf_list.begin(), ref_buf_list.end(),
+                    ref_buf_.at(fb_idx)) == ref_buf_list.end()) {
+        ref_buf_list.push_back(ref_buf_.at(fb_idx));
+      }
     }
 
     if (enc_layer_conf.reference_alt_ref[layer_id.spatial_layer_id]) {
       const size_t fb_idx =
           enc_layer_conf.alt_fb_idx[layer_id.spatial_layer_id];
       RTC_DCHECK(ref_buf_.find(fb_idx) != ref_buf_.end());
-      ref_buf_list.push_back(ref_buf_.at(fb_idx));
+      if (std::find(ref_buf_list.begin(), ref_buf_list.end(),
+                    ref_buf_.at(fb_idx)) == ref_buf_list.end()) {
+        ref_buf_list.push_back(ref_buf_.at(fb_idx));
+      }
     }
 
     if (enc_layer_conf.reference_golden[layer_id.spatial_layer_id]) {
       const size_t fb_idx =
           enc_layer_conf.gld_fb_idx[layer_id.spatial_layer_id];
       RTC_DCHECK(ref_buf_.find(fb_idx) != ref_buf_.end());
-      ref_buf_list.push_back(ref_buf_.at(fb_idx));
+      if (std::find(ref_buf_list.begin(), ref_buf_list.end(),
+                    ref_buf_.at(fb_idx)) == ref_buf_list.end()) {
+        ref_buf_list.push_back(ref_buf_.at(fb_idx));
+      }
     }
   } else if (!is_key_frame) {
     RTC_DCHECK_EQ(num_spatial_layers_, 1);
diff --git a/modules/video_coding/codecs/vp9/vp9_impl.h b/modules/video_coding/codecs/vp9/vp9_impl.h
index 7009311072..d4483060ee 100644
--- a/modules/video_coding/codecs/vp9/vp9_impl.h
+++ b/modules/video_coding/codecs/vp9/vp9_impl.h
@@ -131,6 +131,12 @@ class VP9EncoderImpl : public VP9Encoder {
           spatial_layer_id(spatial_layer_id),
           temporal_layer_id(temporal_layer_id) {}
     RefFrameBuffer() {}
+
+    bool operator==(const RefFrameBuffer& o) {
+      return pic_num == o.pic_num && spatial_layer_id == o.spatial_layer_id &&
+             temporal_layer_id == o.temporal_layer_id;
+    }
+
     size_t pic_num = 0;
     size_t spatial_layer_id = 0;
     size_t temporal_layer_id = 0;