diff --git a/doc/src/sgml/xfunc.sgml b/doc/src/sgml/xfunc.sgml
index d9afd3be4d..7c3cfb0115 100644
--- a/doc/src/sgml/xfunc.sgml
+++ b/doc/src/sgml/xfunc.sgml
@@ -2241,7 +2241,7 @@ PG_FUNCTION_INFO_V1(funcname);
      <function>PG_GETARG_<replaceable>xxx</replaceable>()</function>
      macro that corresponds to the argument's data type.  In non-strict
      functions there needs to be a previous check about argument null-ness
-     using <function>PG_ARGNULL_<replaceable>xxx</replaceable>()</function>.
+     using <function>PG_ARGISNULL_<replaceable>xxx</replaceable>()</function>.
      The result is returned using a
      <function>PG_RETURN_<replaceable>xxx</replaceable>()</function>
      macro for the return type.