diff --git a/libavcodec/truemotion1.c b/libavcodec/truemotion1.c
index 6528a1f391..ed79959240 100644
--- a/libavcodec/truemotion1.c
+++ b/libavcodec/truemotion1.c
@@ -317,12 +317,17 @@ static int truemotion1_decode_header(TrueMotion1Context *s)
     const uint8_t *sel_vector_table;
 
     header.header_size = ((s->buf[0] >> 5) | (s->buf[0] << 3)) & 0x7f;
-    if (s->buf[0] < 0x10 || header.header_size >= s->size)
+    if (s->buf[0] < 0x10)
     {
         av_log(s->avctx, AV_LOG_ERROR, "invalid header size (%d)\n", s->buf[0]);
         return AVERROR_INVALIDDATA;
     }
 
+    if (header.header_size + 1 > s->size) {
+        av_log(s->avctx, AV_LOG_ERROR, "Input packet too small.\n");
+        return AVERROR_INVALIDDATA;
+    }
+
     /* unscramble the header bytes with a XOR operation */
     for (i = 1; i < header.header_size; i++)
         header_buffer[i - 1] = s->buf[i] ^ s->buf[i + 1];