diff --git a/lib/decompress_unlzma.c b/lib/decompress_unlzma.c
index f30c899..476c65a 100644
--- a/lib/decompress_unlzma.c
+++ b/lib/decompress_unlzma.c
@@ -522,6 +522,9 @@
 			cst->rep0 = pos_slot;
 		if (++(cst->rep0) == 0)
 			return 0;
+		if (cst->rep0 > wr->header->dict_size
+				|| cst->rep0 > get_pos(wr))
+			return -1;
 	}
 
 	len += LZMA_MATCH_MIN_LEN;