diff --git a/doc/src/sgml/func.sgml b/doc/src/sgml/func.sgml
index d41c09b68b..6dfa3dc977 100644
--- a/doc/src/sgml/func.sgml
+++ b/doc/src/sgml/func.sgml
@@ -20209,12 +20209,13 @@ postgres=# SELECT * FROM pg_walfile_name_offset(pg_stop_backup());
        <entry><literal><function>pg_partition_tree(<type>oid</type>)</function></literal></entry>
        <entry><type>setof record</type></entry>
        <entry>
-        List information about a partition tree for the given partitioned
-        table, consisting of one row for each partition in a tree.  The
-        information available is the OID of the partition, the OID of its
-        immediate partitioned table, and its level in the hierarchy,
-        beginning at <literal>0</literal> for the top-most parent, and
-        incremented by <literal>1</literal> for each level up.
+        List information about table in a partition tree for a given
+        partitioned table, which consists of one row for each partition and
+        table itself.  Information provided includes the OID of the partition,
+        the OID of its immediate parent, and its level in the hierarchy.
+        The value of level begins at <literal>0</literal> for the input table
+        in its role as the root of the partition tree, <literal>1</literal> for
+        its partitions, <literal>2</literal> for their partitions, and so on.
        </entry>
       </row>
      </tbody>
diff --git a/src/backend/utils/adt/partitionfuncs.c b/src/backend/utils/adt/partitionfuncs.c
index fc0a904967..41c57cac2d 100644
--- a/src/backend/utils/adt/partitionfuncs.c
+++ b/src/backend/utils/adt/partitionfuncs.c
@@ -1,7 +1,7 @@
 /*-------------------------------------------------------------------------
  *
  * partitionfuncs.c
- *		  Functions for accessing partitioning data
+ *		  Functions for accessing partitioning related metadata
  *
  * Portions Copyright (c) 1996-2018, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
diff --git a/src/test/regress/sql/partition_info.sql b/src/test/regress/sql/partition_info.sql
index 2ad75882b0..d9d96a284c 100644
--- a/src/test/regress/sql/partition_info.sql
+++ b/src/test/regress/sql/partition_info.sql
@@ -17,11 +17,24 @@ SELECT relid::regclass, parentrelid::regclass, level,
     pg_relation_size(relid) = 0 AS is_empty
   FROM pg_partition_tree('ptif_test'::regclass);
 
--- children of the main tree
-SELECT relid::regclass, parentrelid::regclass, level
-  FROM pg_partition_tree('ptif_test0'::regclass);
-SELECT relid::regclass, parentrelid::regclass, level
-  FROM pg_partition_tree('ptif_test01'::regclass);
+-- check that it works correctly even if it's passed other tables in the tree
+
+-- passing an intermediate level partitioned table
+SELECT relid::regclass, parentrelid::regclass, level, relkind <> 'p' AS isleaf
+  FROM pg_partition_tree('ptif_test0'::regclass) p
+  JOIN pg_class c ON (p.relid = c.oid);
+
+-- passing a leaf partition
+SELECT relid::regclass, parentrelid::regclass, level, relkind <> 'p' AS isleaf
+  FROM pg_partition_tree('ptif_test01'::regclass) p
+  JOIN pg_class c ON (p.relid = c.oid);
+
+-- check that passing a table that's not part of any partition tree works
+-- the same as passing a leaf partition
+create table ptif_normal_table(a int);
+SELECT relid::regclass, parentrelid::regclass, level, relkind <> 'p' AS isleaf
+  FROM pg_partition_tree('ptif_normal_table'::regclass) p
+  JOIN pg_class c ON (p.relid = c.oid);
 
 -- this results in NULL, as there are no level 1 partitions of a leaf partition
 SELECT sum(pg_relation_size(relid)) AS total_size