diff --git a/doc/filter_design.txt b/doc/filter_design.txt
index fca24a94b5..d784d8471e 100644
--- a/doc/filter_design.txt
+++ b/doc/filter_design.txt
@@ -98,7 +98,7 @@ Buffer references ownership and permissions
     The AVFilterLink structure has a few AVFilterBufferRef fields. The
     cur_buf and out_buf were used with the deprecated
     start_frame/draw_slice/end_frame API and should no longer be used.
-    src_buf, cur_buf_copy and partial_buf are used by libavfilter internally
+    src_buf and partial_buf are used by libavfilter internally
     and must not be accessed by filters.
 
   Reference permissions