diff --git a/libavcodec/h264_parser.c b/libavcodec/h264_parser.c
index 826c17a0f1..bcaa04a115 100644
--- a/libavcodec/h264_parser.c
+++ b/libavcodec/h264_parser.c
@@ -330,6 +330,7 @@ static int init(AVCodecParserContext *s)
 {
     H264Context *h = s->priv_data;
     h->thread_context[0] = h;
+    h->s.slice_context_count = 1;
     return 0;
 }
 
diff --git a/libavcodec/mpeg4video_parser.c b/libavcodec/mpeg4video_parser.c
index 162bc1d03e..89bbf3465d 100644
--- a/libavcodec/mpeg4video_parser.c
+++ b/libavcodec/mpeg4video_parser.c
@@ -99,6 +99,7 @@ static av_cold int mpeg4video_parse_init(AVCodecParserContext *s)
     if (!pc->enc)
         return -1;
     pc->first_picture = 1;
+    pc->enc->slice_context_count = 1;
     return 0;
 }
 
diff --git a/libavcodec/vc1_parser.c b/libavcodec/vc1_parser.c
index e6243d9ac0..0cc5ea0fa8 100644
--- a/libavcodec/vc1_parser.c
+++ b/libavcodec/vc1_parser.c
@@ -184,9 +184,17 @@ static int vc1_split(AVCodecContext *avctx,
     return 0;
 }
 
+static int vc1_parse_init(AVCodecParserContext *s)
+{
+    VC1ParseContext *vpc = s->priv_data;
+    vpc->v.s.slice_context_count = 1;
+    return 0;
+}
+
 AVCodecParser ff_vc1_parser = {
     .codec_ids      = { CODEC_ID_VC1 },
     .priv_data_size = sizeof(VC1ParseContext),
+    .parser_init    = vc1_parse_init,
     .parser_parse   = vc1_parse,
     .parser_close   = ff_parse1_close,
     .split          = vc1_split,