diff --git a/vp9/decoder/vp9_decoder.c b/vp9/decoder/vp9_decoder.c
index 2a2f0f5fa..1a4155825 100644
--- a/vp9/decoder/vp9_decoder.c
+++ b/vp9/decoder/vp9_decoder.c
@@ -123,8 +123,12 @@ vpx_codec_err_t vp9_copy_reference_dec(VP9Decoder *pbi,
    * later commit that adds VP9-specific controls for this functionality.
    */
   if (ref_frame_flag == VP9_LAST_FLAG) {
-    const YV12_BUFFER_CONFIG *const cfg =
-        &cm->frame_bufs[cm->ref_frame_map[0]].buf;
+    const YV12_BUFFER_CONFIG *const cfg = get_ref_frame(cm, 0);
+    if (cfg == NULL) {
+      vpx_internal_error(&cm->error, VPX_CODEC_ERROR,
+                         "No 'last' reference frame");
+      return VPX_CODEC_ERROR;
+    }
     if (!equal_dimensions(cfg, sd))
       vpx_internal_error(&cm->error, VPX_CODEC_ERROR,
                          "Incorrect buffer dimensions");