diff --git a/libavcodec/4xm.c b/libavcodec/4xm.c
index 9350f06e9b..f854f1cfb5 100644
--- a/libavcodec/4xm.c
+++ b/libavcodec/4xm.c
@@ -459,6 +459,11 @@ static int decode_p_frame(FourXContext *f, const uint8_t *buf, int length){
 static int decode_i_block(FourXContext *f, DCTELEM *block){
     int code, i, j, level, val;
 
+    if(get_bits_left(&f->gb) < 2){
+        av_log(f->avctx, AV_LOG_ERROR, "%d bits left before decode_i_block()\n", get_bits_left(&f->gb));
+        return -1;
+    }
+
     /* DC coef */
     val = get_vlc2(&f->pre_gb, f->pre_vlc.table, ACDC_VLC_BITS, 3);
     if (val>>4){