Index: libavcodec/mjpegdec.c
===================================================================
--- libavcodec/mjpegdec.c	(revision 25432)
+++ libavcodec/mjpegdec.c	(working copy)
@@ -406,6 +406,9 @@
     block[0] = val;
     /* AC coefs */
     i = 0;
+    if(s->gb.buffer + s->gb.index/8 >= s->gb.buffer_end){
+        av_log(s->avctx, AV_LOG_ERROR, "decode_block overrun by %u bytes. s->gb.buffer : %p, s->gb.index : %u, s->gb.size_in_bits : %u\n", (s->gb.index-s->gb.size_in_bits)/8,  s->gb.buffer, s->gb.index, s->gb.size_in_bits);
+    }
     {OPEN_READER(re, &s->gb)
     for(;;) {
         UPDATE_CACHE(re, &s->gb);