diff --git a/libavformat/assdec.c b/libavformat/assdec.c
index 5423c03f14..a9a2efac2e 100644
--- a/libavformat/assdec.c
+++ b/libavformat/assdec.c
@@ -125,6 +125,8 @@ static int ass_read_header(AVFormatContext *s)
     av_bprint_init(&line,   0, AV_BPRINT_SIZE_UNLIMITED);
     av_bprint_init(&rline,  0, AV_BPRINT_SIZE_UNLIMITED);
 
+    ass->q.keep_duplicates = 1;
+
     for (;;) {
         int64_t pos = get_line(&line, &tr);
         int64_t ts_start = AV_NOPTS_VALUE;