diff --git a/libavfilter/vf_drawtext.c b/libavfilter/vf_drawtext.c
index dccc534bbc..f3ce7a6f07 100644
--- a/libavfilter/vf_drawtext.c
+++ b/libavfilter/vf_drawtext.c
@@ -1451,13 +1451,14 @@ continue_on_failed:
             s->tab_clusters[tab_idx++] = i;
             *p = ' ';
         }
+        size_t len = p - start;
         GET_UTF8(code, *p ? *p++ : 0, code = 0xfffd; goto continue_on_failed2;);
 continue_on_failed2:
         if (ff_is_newline(code) || code == 0) {
             TextLine *cur_line = &s->lines[line_count];
             HarfbuzzData *hb = &cur_line->hb_data;
             cur_line->cluster_offset = line_offset;
-            ret = shape_text_hb(s, hb, start, p - start);
+            ret = shape_text_hb(s, hb, start, len);
             if (ret != 0) {
                 goto done;
             }