diff --git a/src/backend/utils/adt/ruleutils.c b/src/backend/utils/adt/ruleutils.c
index 8f21eedac4c..81041c46f18 100644
--- a/src/backend/utils/adt/ruleutils.c
+++ b/src/backend/utils/adt/ruleutils.c
@@ -758,7 +758,7 @@ pg_get_triggerdef_worker(Oid trigid, bool pretty)
  *
  * Note that the SQL-function versions of this omit any info about the
  * index tablespace; this is intentional because pg_dump wants it that way.
- * However pg_get_indexdef_string() includes index tablespace if not default.
+ * However pg_get_indexdef_string() includes the index tablespace.
  * ----------
  */
 Datum
@@ -787,7 +787,11 @@ pg_get_indexdef_ext(PG_FUNCTION_ARGS)
 														   prettyFlags)));
 }
 
-/* Internal version that returns a palloc'd C string */
+/*
+ * Internal version for use by ALTER TABLE.
+ * Includes a tablespace clause in the result.
+ * Returns a palloc'd C string; no pretty-printing.
+ */
 char *
 pg_get_indexdef_string(Oid indexrelid)
 {
@@ -1036,20 +1040,19 @@ pg_get_indexdef_worker(Oid indexrelid, int colno,
 		}
 
 		/*
-		 * If it's in a nondefault tablespace, say so, but only if requested
+		 * Print tablespace, but only if requested
 		 */
 		if (showTblSpc)
 		{
 			Oid			tblspc;
 
 			tblspc = get_rel_tablespace(indexrelid);
-			if (OidIsValid(tblspc))
-			{
-				if (isConstraint)
-					appendStringInfoString(&buf, " USING INDEX");
-				appendStringInfo(&buf, " TABLESPACE %s",
-							  quote_identifier(get_tablespace_name(tblspc)));
-			}
+			if (!OidIsValid(tblspc))
+				tblspc = MyDatabaseTableSpace;
+			if (isConstraint)
+				appendStringInfoString(&buf, " USING INDEX");
+			appendStringInfo(&buf, " TABLESPACE %s",
+							 quote_identifier(get_tablespace_name(tblspc)));
 		}
 
 		/*
diff --git a/src/test/regress/input/tablespace.source b/src/test/regress/input/tablespace.source
index dba96f4547f..ecc47124a5d 100644
--- a/src/test/regress/input/tablespace.source
+++ b/src/test/regress/input/tablespace.source
@@ -34,6 +34,37 @@ CREATE INDEX foo_idx on testschema.foo(i) TABLESPACE testspace;
 SELECT relname, spcname FROM pg_catalog.pg_tablespace t, pg_catalog.pg_class c
     where c.reltablespace = t.oid AND c.relname = 'foo_idx';
 
+-- check that default_tablespace doesn't affect ALTER TABLE index rebuilds
+CREATE TABLE testschema.test_default_tab(id bigint) TABLESPACE testspace;
+INSERT INTO testschema.test_default_tab VALUES (1);
+CREATE INDEX test_index1 on testschema.test_default_tab (id);
+CREATE INDEX test_index2 on testschema.test_default_tab (id) TABLESPACE testspace;
+\d testschema.test_index1
+\d testschema.test_index2
+-- use a custom tablespace for default_tablespace
+SET default_tablespace TO testspace;
+-- tablespace should not change if no rewrite
+ALTER TABLE testschema.test_default_tab ALTER id TYPE bigint;
+\d testschema.test_index1
+\d testschema.test_index2
+SELECT * FROM testschema.test_default_tab;
+-- tablespace should not change even if there is an index rewrite
+ALTER TABLE testschema.test_default_tab ALTER id TYPE int;
+\d testschema.test_index1
+\d testschema.test_index2
+SELECT * FROM testschema.test_default_tab;
+-- now use the default tablespace for default_tablespace
+SET default_tablespace TO '';
+-- tablespace should not change if no rewrite
+ALTER TABLE testschema.test_default_tab ALTER id TYPE int;
+\d testschema.test_index1
+\d testschema.test_index2
+-- tablespace should not change even if there is an index rewrite
+ALTER TABLE testschema.test_default_tab ALTER id TYPE bigint;
+\d testschema.test_index1
+\d testschema.test_index2
+DROP TABLE testschema.test_default_tab;
+
 -- let's try moving a table from one place to another
 CREATE TABLE testschema.atable AS VALUES (1), (2);
 CREATE UNIQUE INDEX anindex ON testschema.atable(column1);
diff --git a/src/test/regress/output/tablespace.source b/src/test/regress/output/tablespace.source
index 1260c968880..7b63ad872a4 100644
--- a/src/test/regress/output/tablespace.source
+++ b/src/test/regress/output/tablespace.source
@@ -48,6 +48,111 @@ SELECT relname, spcname FROM pg_catalog.pg_tablespace t, pg_catalog.pg_class c
  foo_idx | testspace
 (1 row)
 
+-- check that default_tablespace doesn't affect ALTER TABLE index rebuilds
+CREATE TABLE testschema.test_default_tab(id bigint) TABLESPACE testspace;
+INSERT INTO testschema.test_default_tab VALUES (1);
+CREATE INDEX test_index1 on testschema.test_default_tab (id);
+CREATE INDEX test_index2 on testschema.test_default_tab (id) TABLESPACE testspace;
+\d testschema.test_index1
+Index "testschema.test_index1"
+ Column |  Type  | Definition 
+--------+--------+------------
+ id     | bigint | id
+btree, for table "testschema.test_default_tab"
+
+\d testschema.test_index2
+Index "testschema.test_index2"
+ Column |  Type  | Definition 
+--------+--------+------------
+ id     | bigint | id
+btree, for table "testschema.test_default_tab"
+Tablespace: "testspace"
+
+-- use a custom tablespace for default_tablespace
+SET default_tablespace TO testspace;
+-- tablespace should not change if no rewrite
+ALTER TABLE testschema.test_default_tab ALTER id TYPE bigint;
+\d testschema.test_index1
+Index "testschema.test_index1"
+ Column |  Type  | Definition 
+--------+--------+------------
+ id     | bigint | id
+btree, for table "testschema.test_default_tab"
+
+\d testschema.test_index2
+Index "testschema.test_index2"
+ Column |  Type  | Definition 
+--------+--------+------------
+ id     | bigint | id
+btree, for table "testschema.test_default_tab"
+Tablespace: "testspace"
+
+SELECT * FROM testschema.test_default_tab;
+ id 
+----
+  1
+(1 row)
+
+-- tablespace should not change even if there is an index rewrite
+ALTER TABLE testschema.test_default_tab ALTER id TYPE int;
+\d testschema.test_index1
+Index "testschema.test_index1"
+ Column |  Type   | Definition 
+--------+---------+------------
+ id     | integer | id
+btree, for table "testschema.test_default_tab"
+
+\d testschema.test_index2
+Index "testschema.test_index2"
+ Column |  Type   | Definition 
+--------+---------+------------
+ id     | integer | id
+btree, for table "testschema.test_default_tab"
+Tablespace: "testspace"
+
+SELECT * FROM testschema.test_default_tab;
+ id 
+----
+  1
+(1 row)
+
+-- now use the default tablespace for default_tablespace
+SET default_tablespace TO '';
+-- tablespace should not change if no rewrite
+ALTER TABLE testschema.test_default_tab ALTER id TYPE int;
+\d testschema.test_index1
+Index "testschema.test_index1"
+ Column |  Type   | Definition 
+--------+---------+------------
+ id     | integer | id
+btree, for table "testschema.test_default_tab"
+
+\d testschema.test_index2
+Index "testschema.test_index2"
+ Column |  Type   | Definition 
+--------+---------+------------
+ id     | integer | id
+btree, for table "testschema.test_default_tab"
+Tablespace: "testspace"
+
+-- tablespace should not change even if there is an index rewrite
+ALTER TABLE testschema.test_default_tab ALTER id TYPE bigint;
+\d testschema.test_index1
+Index "testschema.test_index1"
+ Column |  Type  | Definition 
+--------+--------+------------
+ id     | bigint | id
+btree, for table "testschema.test_default_tab"
+
+\d testschema.test_index2
+Index "testschema.test_index2"
+ Column |  Type  | Definition 
+--------+--------+------------
+ id     | bigint | id
+btree, for table "testschema.test_default_tab"
+Tablespace: "testspace"
+
+DROP TABLE testschema.test_default_tab;
 -- let's try moving a table from one place to another
 CREATE TABLE testschema.atable AS VALUES (1), (2);
 CREATE UNIQUE INDEX anindex ON testschema.atable(column1);