diff --git a/doc/src/sgml/catalogs.sgml b/doc/src/sgml/catalogs.sgml
index c1d11be73f..216aa4510d 100644
--- a/doc/src/sgml/catalogs.sgml
+++ b/doc/src/sgml/catalogs.sgml
@@ -9305,6 +9305,10 @@ SCRAM-SHA-256$<replaceable>&lt;iteration count&gt;</replaceable>:<replaceable>&l
       <entry><literal>X</literal></entry>
       <entry><type>unknown</type> type</entry>
      </row>
+     <row>
+      <entry><literal>Z</literal></entry>
+      <entry>Internal-use types</entry>
+     </row>
     </tbody>
    </tgroup>
   </table>
diff --git a/src/include/catalog/pg_type.dat b/src/include/catalog/pg_type.dat
index 41074c994b..14d50376a1 100644
--- a/src/include/catalog/pg_type.dat
+++ b/src/include/catalog/pg_type.dat
@@ -145,24 +145,24 @@
   typsend => 'xml_send', typalign => 'i', typstorage => 'x' },
 { oid => '194', descr => 'string representing an internal node tree',
   typname => 'pg_node_tree', typlen => '-1', typbyval => 'f',
-  typcategory => 'S', typinput => 'pg_node_tree_in',
+  typcategory => 'Z', typinput => 'pg_node_tree_in',
   typoutput => 'pg_node_tree_out', typreceive => 'pg_node_tree_recv',
   typsend => 'pg_node_tree_send', typalign => 'i', typstorage => 'x',
   typcollation => 'default' },
 { oid => '3361', descr => 'multivariate ndistinct coefficients',
   typname => 'pg_ndistinct', typlen => '-1', typbyval => 'f',
-  typcategory => 'S', typinput => 'pg_ndistinct_in',
+  typcategory => 'Z', typinput => 'pg_ndistinct_in',
   typoutput => 'pg_ndistinct_out', typreceive => 'pg_ndistinct_recv',
   typsend => 'pg_ndistinct_send', typalign => 'i', typstorage => 'x',
   typcollation => 'default' },
 { oid => '3402', descr => 'multivariate dependencies',
   typname => 'pg_dependencies', typlen => '-1', typbyval => 'f',
-  typcategory => 'S', typinput => 'pg_dependencies_in',
+  typcategory => 'Z', typinput => 'pg_dependencies_in',
   typoutput => 'pg_dependencies_out', typreceive => 'pg_dependencies_recv',
   typsend => 'pg_dependencies_send', typalign => 'i', typstorage => 'x',
   typcollation => 'default' },
 { oid => '5017', descr => 'multivariate MCV list',
-  typname => 'pg_mcv_list', typlen => '-1', typbyval => 'f', typcategory => 'S',
+  typname => 'pg_mcv_list', typlen => '-1', typbyval => 'f', typcategory => 'Z',
   typinput => 'pg_mcv_list_in', typoutput => 'pg_mcv_list_out',
   typreceive => 'pg_mcv_list_recv', typsend => 'pg_mcv_list_send',
   typalign => 'i', typstorage => 'x', typcollation => 'default' },
@@ -681,13 +681,13 @@
   typalign => 'd', typstorage => 'x' },
 { oid => '4600', descr => 'BRIN bloom summary',
   typname => 'pg_brin_bloom_summary', typlen => '-1', typbyval => 'f',
-  typcategory => 'S', typinput => 'brin_bloom_summary_in',
+  typcategory => 'Z', typinput => 'brin_bloom_summary_in',
   typoutput => 'brin_bloom_summary_out',
   typreceive => 'brin_bloom_summary_recv', typsend => 'brin_bloom_summary_send',
   typalign => 'i', typstorage => 'x', typcollation => 'default' },
 { oid => '4601', descr => 'BRIN minmax-multi summary',
   typname => 'pg_brin_minmax_multi_summary', typlen => '-1', typbyval => 'f',
-  typcategory => 'S', typinput => 'brin_minmax_multi_summary_in',
+  typcategory => 'Z', typinput => 'brin_minmax_multi_summary_in',
   typoutput => 'brin_minmax_multi_summary_out',
   typreceive => 'brin_minmax_multi_summary_recv',
   typsend => 'brin_minmax_multi_summary_send', typalign => 'i',
diff --git a/src/include/catalog/pg_type.h b/src/include/catalog/pg_type.h
index e568e21dee..5e891a0596 100644
--- a/src/include/catalog/pg_type.h
+++ b/src/include/catalog/pg_type.h
@@ -294,6 +294,7 @@ DECLARE_UNIQUE_INDEX(pg_type_typname_nsp_index, 2704, TypeNameNspIndexId, on pg_
 #define  TYPCATEGORY_USER		'U'
 #define  TYPCATEGORY_BITSTRING	'V' /* er ... "varbit"? */
 #define  TYPCATEGORY_UNKNOWN	'X'
+#define  TYPCATEGORY_INTERNAL	'Z'
 
 #define  TYPALIGN_CHAR			'c' /* char alignment (i.e. unaligned) */
 #define  TYPALIGN_SHORT			's' /* short alignment (typically 2 bytes) */