diff --git a/libavcodec/truemotion1.c b/libavcodec/truemotion1.c
index bcfe473852..b6481cbd7c 100644
--- a/libavcodec/truemotion1.c
+++ b/libavcodec/truemotion1.c
@@ -444,6 +444,8 @@ static int truemotion1_decode_header(TrueMotion1Context *s)
     if (s->flags & FLAG_KEYFRAME) {
         /* no change bits specified for a keyframe; only index bytes */
         s->index_stream = s->mb_change_bits;
+        if (s->avctx->width * s->avctx->height / 2048 + header.header_size > s->size)
+            return AVERROR_INVALIDDATA;
     } else {
         /* one change bit per 4x4 block */
         s->index_stream = s->mb_change_bits +