diff --git a/libavformat/subviewerdec.c b/libavformat/subviewerdec.c
index 25fe7ac9a6..94817c04e9 100644
--- a/libavformat/subviewerdec.c
+++ b/libavformat/subviewerdec.c
@@ -138,6 +138,10 @@ static int subviewer_read_header(AVFormatContext *s)
             new_event = 1;
             pos = avio_tell(s->pb);
         } else if (*line) {
+            if (pts_start == AV_NOPTS_VALUE) {
+                res = AVERROR_INVALIDDATA;
+                goto end;
+            }
             if (!new_event) {
                 sub = ff_subtitles_queue_insert(&subviewer->q, "\n", 1, 1);
                 if (!sub) {