diff --git a/libavutil/tx.c b/libavutil/tx.c
index a90ccffcc4..573f4863d1 100644
--- a/libavutil/tx.c
+++ b/libavutil/tx.c
@@ -606,7 +606,8 @@ av_cold int ff_tx_init_subtx(AVTXContext *s, enum AVTXType type,
             break;
     }
 
-    av_freep(&s->sub);
+    if (!s->nb_sub)
+        av_freep(&s->sub);
 
 end:
     av_free(cd_matches);