diff --git a/libavformat/matroskadec.c b/libavformat/matroskadec.c
index 9917b04876..64a66a53ab 100644
--- a/libavformat/matroskadec.c
+++ b/libavformat/matroskadec.c
@@ -81,6 +81,7 @@ typedef const struct EbmlSyntax {
     int list_elem_size;
     int data_offset;
     union {
+        int64_t     i;
         uint64_t    u;
         double      f;
         const char *s;
@@ -582,7 +583,7 @@ static EbmlSyntax matroska_blockgroup[] = {
     { MATROSKA_ID_SIMPLEBLOCK,    EBML_BIN,  0, offsetof(MatroskaBlock, bin) },
     { MATROSKA_ID_BLOCKDURATION,  EBML_UINT, 0, offsetof(MatroskaBlock, duration) },
     { MATROSKA_ID_DISCARDPADDING, EBML_SINT, 0, offsetof(MatroskaBlock, discard_padding) },
-    { MATROSKA_ID_BLOCKREFERENCE, EBML_SINT, 0, offsetof(MatroskaBlock, reference) },
+    { MATROSKA_ID_BLOCKREFERENCE, EBML_SINT, 0, offsetof(MatroskaBlock, reference), { .i = INT64_MIN } },
     { MATROSKA_ID_CODECSTATE,     EBML_NONE },
     {                          1, EBML_UINT, 0, offsetof(MatroskaBlock, non_simple), { .u = 1 } },
     { 0 }
@@ -952,6 +953,9 @@ static int ebml_parse_nest(MatroskaDemuxContext *matroska, EbmlSyntax *syntax,
 
     for (i = 0; syntax[i].id; i++)
         switch (syntax[i].type) {
+        case EBML_SINT:
+            *(int64_t *) ((char *) data + syntax[i].data_offset) = syntax[i].def.i;
+            break;
         case EBML_UINT:
             *(uint64_t *) ((char *) data + syntax[i].data_offset) = syntax[i].def.u;
             break;
@@ -2862,7 +2866,7 @@ static int matroska_parse_cluster_incremental(MatroskaDemuxContext *matroska)
         matroska->current_cluster_num_blocks = blocks_list->nb_elem;
         i                                    = blocks_list->nb_elem - 1;
         if (blocks[i].bin.size > 0 && blocks[i].bin.data) {
-            int is_keyframe = blocks[i].non_simple ? !blocks[i].reference : -1;
+            int is_keyframe = blocks[i].non_simple ? blocks[i].reference == INT64_MIN : -1;
             uint8_t* additional = blocks[i].additional.size > 0 ?
                                     blocks[i].additional.data : NULL;
             if (!blocks[i].non_simple)
@@ -2900,7 +2904,7 @@ static int matroska_parse_cluster(MatroskaDemuxContext *matroska)
     blocks      = blocks_list->elem;
     for (i = 0; i < blocks_list->nb_elem; i++)
         if (blocks[i].bin.size > 0 && blocks[i].bin.data) {
-            int is_keyframe = blocks[i].non_simple ? !blocks[i].reference : -1;
+            int is_keyframe = blocks[i].non_simple ? blocks[i].reference == INT64_MIN : -1;
             res = matroska_parse_block(matroska, blocks[i].bin.data,
                                        blocks[i].bin.size, blocks[i].bin.pos,
                                        cluster.timecode, blocks[i].duration,