diff --git a/createas.c b/createas.c
index 4595a70..efe777c 100644
--- a/createas.c
+++ b/createas.c
@@ -711,7 +711,7 @@ check_ivm_restriction_walker(Node *node, check_ivm_restriction_context *context)
 				if (qry->havingQual != NULL)
 					ereport(ERROR,
 							(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
-							 errmsg(" HAVING clause is not supported on incrementally maintainable materialized view")));
+							 errmsg("HAVING clause is not supported on incrementally maintainable materialized view")));
 				if (qry->sortClause != NIL)	/* There is a possibility that we don't need to return an error */
 					ereport(ERROR,
 							(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
@@ -744,11 +744,6 @@ check_ivm_restriction_walker(Node *node, check_ivm_restriction_context *context)
 					ereport(ERROR,
 							(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
 							 errmsg("FOR UPDATE/SHARE clause is not supported on incrementally maintainable materialized view")));
-				if (qry->hasSubLinks && context->sublevels_up > 0)
-					ereport(ERROR,
-							(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
-							 errmsg("this query is not allowed on incrementally maintainable materialized view"),
-							 errhint("Only simple subquery is supported")));
 
 				/* system column restrictions */
 				vars = pull_vars_of_level((Node *) qry, 0);
@@ -831,7 +826,7 @@ check_ivm_restriction_walker(Node *node, check_ivm_restriction_context *context)
 					}
 				}
 
-				query_tree_walker(qry, check_ivm_restriction_walker, (void *) context, QTW_IGNORE_RANGE_TABLE);
+				query_tree_walker(qry, check_ivm_restriction_walker, (void *) context, QTW_IGNORE_RT_SUBQUERIES);
 
 				break;
 			}
@@ -847,12 +842,6 @@ check_ivm_restriction_walker(Node *node, check_ivm_restriction_context *context)
 							(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
 							 errmsg("expression containing an aggregate in it is not supported on incrementally maintainable materialized view")));
 
-				if (IsA(tle->expr, SubLink))
-					ereport(ERROR,
-							(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
-							 errmsg("this query is not allowed on incrementally maintainable materialized view"),
-							 errhint("subquery is not supported in targetlist")));
-
 				expression_tree_walker(node, check_ivm_restriction_walker, (void *) context);
 				break;
 			}
@@ -865,7 +854,7 @@ check_ivm_restriction_walker(Node *node, check_ivm_restriction_context *context)
 								(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
 								 errmsg("OUTER JOIN is not supported on incrementally maintainable materialized view")));
 
-				expression_tree_walker(node, check_ivm_restriction_walker, NULL);
+				expression_tree_walker(node, check_ivm_restriction_walker, (void *) context);
 				break;
 			}
 		case T_Aggref:
@@ -893,15 +882,16 @@ check_ivm_restriction_walker(Node *node, check_ivm_restriction_context *context)
 					ereport(ERROR,
 							(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
 							 errmsg("aggregate function %s is not supported on incrementally maintainable materialized view", aggname)));
+
+				expression_tree_walker(node, check_ivm_restriction_walker, (void *) context);
 				break;
 			}
 		case T_SubLink:
 			{
-				/* Now, EXISTS clause is supported only */
 				ereport(ERROR,
 						(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
-						 errmsg("this query is not allowed on incrementally maintainable materialized view"),
-						 errhint("Only simple subquery is supported")));
+						 errmsg("unsupported subquery on incrementally maintainable materialized view"),
+						 errhint("Only simple subquery in FROM clause is supported.")));
 				break;
 			}
 		default:
diff --git a/expected/pg_ivm.out b/expected/pg_ivm.out
index 5b57551..e8f56f1 100644
--- a/expected/pg_ivm.out
+++ b/expected/pg_ivm.out
@@ -662,10 +662,6 @@ SELECT * FROM mv_ri ORDER BY i2;
 (2 rows)
 
 ROLLBACK;
--- not support subquery for using EXISTS()
-SELECT create_immv('mv_ivm_exists_subquery', 'SELECT a.i, a.j FROM mv_base_a a WHERE EXISTS(SELECT 1 FROM mv_base_b b WHERE a.i = b.i)');
-ERROR:  this query is not allowed on incrementally maintainable materialized view
-HINT:  Only simple subquery is supported
 -- support simple subquery in FROM clause
 BEGIN;
 SELECT create_immv('mv_ivm_subquery', 'SELECT a.i,a.j FROM mv_base_a a,( SELECT * FROM mv_base_b) b WHERE a.i = b.i');
@@ -691,6 +687,26 @@ SELECT * FROM mv_ivm_subquery ORDER BY i,j;
 (6 rows)
 
 ROLLBACK;
+-- disallow non-simple subqueries
+SELECT create_immv('mv_ivm_exists_subquery', 'SELECT a.i, a.j FROM mv_base_a a WHERE EXISTS(SELECT 1 FROM mv_base_b b WHERE a.i = b.i)');
+ERROR:  unsupported subquery on incrementally maintainable materialized view
+HINT:  Only simple subquery in FROM clause is supported.
+SELECT create_immv('mv_ivm_subquery', 'SELECT a.i,a.j FROM mv_base_a a, (SELECT i, COUNT(*) FROM mv_base_b GROUP BY i) b WHERE a.i = b.i');
+ERROR:  aggregate functions in nested query are not supported on incrementally maintainable materialized view
+SELECT create_immv('mv_ivm_subquery', 'SELECT a.i,a.j FROM mv_base_a a, (SELECT DISTINCT i FROM mv_base_b) b WHERE a.i = b.i');
+ERROR:  DISTINCT clause in nested query are not supported on incrementally maintainable materialized view
+SELECT create_immv('mv_ivm_subquery', 'SELECT i,j FROM mv_base_a WHERE i IN (SELECT i FROM mv_base_b WHERE k < 103 )');
+ERROR:  unsupported subquery on incrementally maintainable materialized view
+HINT:  Only simple subquery in FROM clause is supported.
+SELECT create_immv('mv_ivm_subquery', 'SELECT i,j, (SELECT k FROM mv_base_b LIMIT 1) FROM mv_base_a a');
+ERROR:  unsupported subquery on incrementally maintainable materialized view
+HINT:  Only simple subquery in FROM clause is supported.
+SELECT create_immv('mv_ivm_subquery', 'SELECT i,j, (SELECT k FROM mv_base_b LIMIT 1) + 1 FROM mv_base_a a');
+ERROR:  unsupported subquery on incrementally maintainable materialized view
+HINT:  Only simple subquery in FROM clause is supported.
+SELECT create_immv('mv_ivm_subquery', 'SELECT * FROM generate_series(1, (SELECT k FROM mv_base_b LIMIT 1)) AS v');
+ERROR:  unsupported subquery on incrementally maintainable materialized view
+HINT:  Only simple subquery in FROM clause is supported.
 -- support join subquery in FROM clause
 BEGIN;
 SELECT create_immv('mv_ivm_join_subquery', 'SELECT i, j, k FROM ( SELECT i, a.j, b.k FROM mv_base_b b INNER JOIN mv_base_a a USING(i)) tmp');
@@ -914,21 +930,12 @@ SELECT create_immv('mv_ivm03', 'SELECT i,j,xmin::text AS x_min FROM mv_base_a');
 ERROR:  system column is not supported on incrementally maintainable materialized view
 SELECT create_immv('mv_ivm04', 'SELECT i,j,xidsend(xmin) AS x_min FROM mv_base_a');
 ERROR:  system column is not supported on incrementally maintainable materialized view
--- contain subquery
-SELECT create_immv('mv_ivm03', 'SELECT i,j FROM mv_base_a WHERE i IN (SELECT i FROM mv_base_b WHERE k < 103 )');
-ERROR:  this query is not allowed on incrementally maintainable materialized view
-HINT:  Only simple subquery is supported
-SELECT create_immv('mv_ivm04', 'SELECT a.i,a.j FROM mv_base_a a, (SELECT DISTINCT i FROM mv_base_b) b WHERE a.i = b.i');
-ERROR:  DISTINCT clause in nested query are not supported on incrementally maintainable materialized view
-SELECT create_immv('mv_ivm05', 'SELECT i,j, (SELECT k FROM mv_base_b b WHERE a.i = b.i) FROM mv_base_a a');
-ERROR:  this query is not allowed on incrementally maintainable materialized view
-HINT:  subquery is not supported in targetlist
 -- contain ORDER BY
 SELECT create_immv('mv_ivm07', 'SELECT i,j,k FROM mv_base_a a INNER JOIN mv_base_b b USING(i) ORDER BY i,j,k');
 ERROR:  ORDER BY clause is not supported on incrementally maintainable materialized view
 -- contain HAVING
 SELECT create_immv('mv_ivm08', 'SELECT i,j,k FROM mv_base_a a INNER JOIN mv_base_b b USING(i) GROUP BY i,j,k HAVING SUM(i) > 5');
-ERROR:   HAVING clause is not supported on incrementally maintainable materialized view
+ERROR:  HAVING clause is not supported on incrementally maintainable materialized view
 -- contain GROUP BY without aggregate
 SELECT create_immv('mv_ivm08', 'SELECT i,j FROM mv_base_a GROUP BY i,j');
 ERROR:  GROUP BY clause without aggregate is not supported on incrementally maintainable materialized view
@@ -939,8 +946,6 @@ SELECT create_immv('mv_ivm07', 'SELECT a.i,a.j FROM mv_base_a a,b_view b WHERE a
 ERROR:  VIEW or MATERIALIZED VIEW is not supported on incrementally maintainable materialized view
 SELECT create_immv('mv_ivm08', 'SELECT a.i,a.j FROM mv_base_a a,b_mview b WHERE a.i = b.i');
 ERROR:  VIEW or MATERIALIZED VIEW is not supported on incrementally maintainable materialized view
-SELECT create_immv('mv_ivm09', 'SELECT a.i,a.j FROM mv_base_a a, (SELECT i, COUNT(*) FROM mv_base_b GROUP BY i) b WHERE a.i = b.i');
-ERROR:  aggregate functions in nested query are not supported on incrementally maintainable materialized view
 -- contain mutable functions
 SELECT create_immv('mv_ivm12', 'SELECT i,j FROM mv_base_a WHERE i = random()::int');
 ERROR:  mutable function is not supported on incrementally maintainable materialized view
diff --git a/sql/pg_ivm.sql b/sql/pg_ivm.sql
index f07ebef..9c4dfec 100644
--- a/sql/pg_ivm.sql
+++ b/sql/pg_ivm.sql
@@ -227,9 +227,6 @@ DELETE FROM ri1 WHERE i=2;
 SELECT * FROM mv_ri ORDER BY i2;
 ROLLBACK;
 
--- not support subquery for using EXISTS()
-SELECT create_immv('mv_ivm_exists_subquery', 'SELECT a.i, a.j FROM mv_base_a a WHERE EXISTS(SELECT 1 FROM mv_base_b b WHERE a.i = b.i)');
-
 -- support simple subquery in FROM clause
 BEGIN;
 SELECT create_immv('mv_ivm_subquery', 'SELECT a.i,a.j FROM mv_base_a a,( SELECT * FROM mv_base_b) b WHERE a.i = b.i');
@@ -239,6 +236,15 @@ SELECT * FROM mv_ivm_subquery ORDER BY i,j;
 
 ROLLBACK;
 
+-- disallow non-simple subqueries
+SELECT create_immv('mv_ivm_exists_subquery', 'SELECT a.i, a.j FROM mv_base_a a WHERE EXISTS(SELECT 1 FROM mv_base_b b WHERE a.i = b.i)');
+SELECT create_immv('mv_ivm_subquery', 'SELECT a.i,a.j FROM mv_base_a a, (SELECT i, COUNT(*) FROM mv_base_b GROUP BY i) b WHERE a.i = b.i');
+SELECT create_immv('mv_ivm_subquery', 'SELECT a.i,a.j FROM mv_base_a a, (SELECT DISTINCT i FROM mv_base_b) b WHERE a.i = b.i');
+SELECT create_immv('mv_ivm_subquery', 'SELECT i,j FROM mv_base_a WHERE i IN (SELECT i FROM mv_base_b WHERE k < 103 )');
+SELECT create_immv('mv_ivm_subquery', 'SELECT i,j, (SELECT k FROM mv_base_b LIMIT 1) FROM mv_base_a a');
+SELECT create_immv('mv_ivm_subquery', 'SELECT i,j, (SELECT k FROM mv_base_b LIMIT 1) + 1 FROM mv_base_a a');
+SELECT create_immv('mv_ivm_subquery', 'SELECT * FROM generate_series(1, (SELECT k FROM mv_base_b LIMIT 1)) AS v');
+
 -- support join subquery in FROM clause
 BEGIN;
 SELECT create_immv('mv_ivm_join_subquery', 'SELECT i, j, k FROM ( SELECT i, a.j, b.k FROM mv_base_b b INNER JOIN mv_base_a a USING(i)) tmp');
@@ -352,10 +358,6 @@ SELECT create_immv('mv_ivm02', 'SELECT i,j FROM mv_base_a WHERE xmin = ''610''')
 SELECT create_immv('mv_ivm03', 'SELECT i,j,xmin::text AS x_min FROM mv_base_a');
 SELECT create_immv('mv_ivm04', 'SELECT i,j,xidsend(xmin) AS x_min FROM mv_base_a');
 
--- contain subquery
-SELECT create_immv('mv_ivm03', 'SELECT i,j FROM mv_base_a WHERE i IN (SELECT i FROM mv_base_b WHERE k < 103 )');
-SELECT create_immv('mv_ivm04', 'SELECT a.i,a.j FROM mv_base_a a, (SELECT DISTINCT i FROM mv_base_b) b WHERE a.i = b.i');
-SELECT create_immv('mv_ivm05', 'SELECT i,j, (SELECT k FROM mv_base_b b WHERE a.i = b.i) FROM mv_base_a a');
 -- contain ORDER BY
 SELECT create_immv('mv_ivm07', 'SELECT i,j,k FROM mv_base_a a INNER JOIN mv_base_b b USING(i) ORDER BY i,j,k');
 -- contain HAVING
@@ -368,7 +370,6 @@ CREATE VIEW b_view AS SELECT i,k FROM mv_base_b;
 CREATE MATERIALIZED VIEW b_mview AS SELECT i,k FROM mv_base_b;
 SELECT create_immv('mv_ivm07', 'SELECT a.i,a.j FROM mv_base_a a,b_view b WHERE a.i = b.i');
 SELECT create_immv('mv_ivm08', 'SELECT a.i,a.j FROM mv_base_a a,b_mview b WHERE a.i = b.i');
-SELECT create_immv('mv_ivm09', 'SELECT a.i,a.j FROM mv_base_a a, (SELECT i, COUNT(*) FROM mv_base_b GROUP BY i) b WHERE a.i = b.i');
 
 -- contain mutable functions
 SELECT create_immv('mv_ivm12', 'SELECT i,j FROM mv_base_a WHERE i = random()::int');