diff --git a/doc/filters.texi b/doc/filters.texi
index 618eb28e28..bd93e0ab84 100644
--- a/doc/filters.texi
+++ b/doc/filters.texi
@@ -1090,9 +1090,9 @@ Set coefficients format.
 transfer function
 @item zp
 Z-plane zeros/poles, cartesian (default)
-@item zpr
+@item pr
 Z-plane zeros/poles, polar radians
-@item zpd
+@item pd
 Z-plane zeros/poles, polar degrees
 @end table