diff --git a/doc/internals/filters.txt b/doc/internals/filters.txt
index 1e4d40a..75c640c 100644
--- a/doc/internals/filters.txt
+++ b/doc/internals/filters.txt
@@ -1207,14 +1207,14 @@
         if (avail > 10 and /* ...Some condition... */) {
             /* Move the buffer forward to have buf->p pointing on unparsed
              * data */
-            b_adv(msg->chn->buf, flt_rsp_nxt(filter));
+            c_adv(msg->chn, flt_rsp_nxt(filter));
 
             /* Skip first 10 bytes. To simplify this example, we consider a
              * non-wrapping buffer  */
             memmove(buf->p + 10, buf->p, avail - 10);
 
             /* Restore buf->p value */
-            b_rew(msg->chn->buf, flt_rsp_nxt(filter));
+            c_rew(msg->chn, flt_rsp_nxt(filter));
 
             /* Now update other filters */
             flt_change_next_size(filter, msg->chn, -10);
@@ -1240,14 +1240,14 @@
         if (len > 10 and /* ...Some condition... */) {
             /* Move the buffer forward to have buf->p pointing on non-forwarded
              * data */
-            b_adv(msg->chn->buf, flt_rsp_fwd(filter));
+            c_adv(msg->chn, flt_rsp_fwd(filter));
 
             /* Skip first 10 bytes. To simplify this example, we consider a
              * non-wrapping buffer  */
             memmove(buf->p + 10, buf->p, len - 10);
 
             /* Restore buf->p value */
-            b_rew(msg->chn->buf, flt_rsp_fwd(filter));
+            c_rew(msg->chn, flt_rsp_fwd(filter));
 
             /* Now update other filters */
             flt_change_forward_size(filter, msg->chn, -10);