diff --git a/doc/src/sgml/func.sgml b/doc/src/sgml/func.sgml
index 93b0bc2bc6..b3687b3645 100644
--- a/doc/src/sgml/func.sgml
+++ b/doc/src/sgml/func.sgml
@@ -25129,6 +25129,29 @@ SELECT pg_type_is_visible('myschema.widget'::regtype);
        </para></entry>
       </row>
 
+      <row>
+       <entry role="func_table_entry"><para role="func_signature">
+        <indexterm>
+         <primary>pg_basetype</primary>
+        </indexterm>
+        <function>pg_basetype</function> ( <type>regtype</type> )
+        <returnvalue>regtype</returnvalue>
+       </para>
+       <para>
+        Returns the OID of the base type of a domain identified by its
+        type OID.  If the argument is not the OID of a domain type,
+        returns the argument as-is.  If there's a chain of domain
+        dependencies, it will recurse until finding the base type.
+       </para>
+       <para>
+        Assuming <literal>CREATE DOMAIN mytext AS text</literal>:
+       </para>
+       <para>
+        <literal>pg_basetype('mytext'::regtype)</literal>
+        <returnvalue>text</returnvalue>
+       </para></entry>
+      </row>
+
       <row>
        <entry id="pg-char-to-encoding" role="func_table_entry"><para role="func_signature">
         <indexterm>
diff --git a/src/backend/utils/adt/misc.c b/src/backend/utils/adt/misc.c
index d4a92d0b3f..d2b4ba8a72 100644
--- a/src/backend/utils/adt/misc.c
+++ b/src/backend/utils/adt/misc.c
@@ -44,6 +44,7 @@
 #include "utils/fmgroids.h"
 #include "utils/lsyscache.h"
 #include "utils/ruleutils.h"
+#include "utils/syscache.h"
 #include "utils/timestamp.h"
 
 
@@ -566,6 +567,48 @@ pg_typeof(PG_FUNCTION_ARGS)
 }
 
 
+/*
+ * Return the base type of the argument.
+ *		If the given type is a domain, return its base type;
+ *		otherwise return the type's own OID.
+ *
+ * This is a SQL-callable version of getBaseType().  Unlike that function,
+ * we don't want to fail for a bogus type OID; this is helpful to keep race
+ * conditions from turning into query failures when scanning the catalogs.
+ * Hence we need our own implementation.
+ */
+Datum
+pg_basetype(PG_FUNCTION_ARGS)
+{
+	Oid			typid = PG_GETARG_OID(0);
+
+	/*
+	 * We loop to find the bottom base type in a stack of domains.
+	 */
+	for (;;)
+	{
+		HeapTuple	tup;
+		Form_pg_type typTup;
+
+		tup = SearchSysCache1(TYPEOID, ObjectIdGetDatum(typid));
+		if (!HeapTupleIsValid(tup))
+			break;				/* return the bogus OID as-is */
+		typTup = (Form_pg_type) GETSTRUCT(tup);
+		if (typTup->typtype != TYPTYPE_DOMAIN)
+		{
+			/* Not a domain, so done */
+			ReleaseSysCache(tup);
+			break;
+		}
+
+		typid = typTup->typbasetype;
+		ReleaseSysCache(tup);
+	}
+
+	PG_RETURN_OID(typid);
+}
+
+
 /*
  * Implementation of the COLLATE FOR expression; returns the collation
  * of the argument.
diff --git a/src/include/catalog/pg_proc.dat b/src/include/catalog/pg_proc.dat
index 07023ee61d..134e3b22fd 100644
--- a/src/include/catalog/pg_proc.dat
+++ b/src/include/catalog/pg_proc.dat
@@ -3889,6 +3889,9 @@
 { oid => '1619', descr => 'type of the argument',
   proname => 'pg_typeof', proisstrict => 'f', provolatile => 's',
   prorettype => 'regtype', proargtypes => 'any', prosrc => 'pg_typeof' },
+{ oid => '8312', descr => 'base type of a domain type',
+  proname => 'pg_basetype', provolatile => 's', prorettype => 'regtype',
+  proargtypes => 'regtype', prosrc => 'pg_basetype' },
 { oid => '3162',
   descr => 'collation of the argument; implementation of the COLLATION FOR expression',
   proname => 'pg_collation_for', proisstrict => 'f', provolatile => 's',
diff --git a/src/test/regress/expected/domain.out b/src/test/regress/expected/domain.out
index dc58793e3f..71d9f1952c 100644
--- a/src/test/regress/expected/domain.out
+++ b/src/test/regress/expected/domain.out
@@ -1292,3 +1292,28 @@ SELECT * FROM information_schema.check_constraints
  regression         | public            | pos_int_not_null | VALUE IS NOT NULL
 (4 rows)
 
+--
+-- Get the base type of a domain
+--
+create domain mytext as text;
+create domain mytext_child_1 as mytext;
+select pg_basetype('mytext'::regtype);
+ pg_basetype 
+-------------
+ text
+(1 row)
+
+select pg_basetype('mytext_child_1'::regtype);
+ pg_basetype 
+-------------
+ text
+(1 row)
+
+select pg_basetype(1);  -- expect 1 not error
+ pg_basetype 
+-------------
+ 1
+(1 row)
+
+drop domain mytext cascade;
+NOTICE:  drop cascades to type mytext_child_1
diff --git a/src/test/regress/sql/domain.sql b/src/test/regress/sql/domain.sql
index ae1b7fbf97..8a5121b056 100644
--- a/src/test/regress/sql/domain.sql
+++ b/src/test/regress/sql/domain.sql
@@ -862,3 +862,15 @@ SELECT * FROM information_schema.check_constraints
             FROM information_schema.domain_constraints
             WHERE domain_name IN ('con', 'dom', 'pos_int', 'things'))
   ORDER BY constraint_name;
+
+--
+-- Get the base type of a domain
+--
+create domain mytext as text;
+create domain mytext_child_1 as mytext;
+
+select pg_basetype('mytext'::regtype);
+select pg_basetype('mytext_child_1'::regtype);
+select pg_basetype(1);  -- expect 1 not error
+
+drop domain mytext cascade;