diff --git a/preprocessing.c b/preprocessing.c
index 954120a2..9de7acfd 100644
--- a/preprocessing.c
+++ b/preprocessing.c
@@ -316,10 +316,11 @@ aqo_planner(Query *parse, const char *query_string, int cursorOptions,
 			disable_aqo_for_query();
 
 			/*
-			 * Switch AQO to controlled mode. In this mode we wouldn't add new
-			 * query classes, just use and learn on existed set.
+			 * Switch AQO to frozen mode. In this mode we wouldn't collect
+			 * any new data, just read collected statistics for already
+			 * known query classes.
 			 */
-			aqo_mode = AQO_MODE_CONTROLLED;
+			aqo_mode = AQO_MODE_FROZEN;
 		}
 	}
 
diff --git a/t/006_overflow.pl b/t/006_overflow.pl
new file mode 100644
index 00000000..eb2d71b9
--- /dev/null
+++ b/t/006_overflow.pl
@@ -0,0 +1,47 @@
+use strict;
+use warnings;
+
+use PostgreSQL::Test::Cluster;
+use PostgreSQL::Test::Utils;
+use Test::More tests => 4;
+
+my $node = PostgreSQL::Test::Cluster->new('aqotest');
+$node->init;
+$node->append_conf('postgresql.conf', qq{
+	shared_preload_libraries = 'aqo'
+	aqo.join_threshold = 0
+	aqo.mode = 'frozen'
+	aqo.show_details = 'on'
+	aqo.dsm_size_max = 10
+	aqo.force_collect_stat = 'on'
+	aqo.fs_max_items = 3
+	aqo.fss_max_items = 10
+});
+
+# General purpose variables.
+my $res;
+my $mode;
+
+# Disable default settings, forced by PGOPTIONS in AQO Makefile
+$ENV{PGOPTIONS}="";
+
+$node->start();
+$node->safe_psql('postgres', 'CREATE EXTENSION aqo');
+
+$mode = $node->safe_psql('postgres',"show aqo.mode");
+like($mode, qr/frozen/);
+
+$node->safe_psql('postgres', 'CREATE TABLE a (x int);
+INSERT INTO a (x) SELECT mod(ival,10) FROM generate_series(1,1000) As ival');
+
+$res = $node->safe_psql('postgres', 'EXPLAIN ANALYZE SELECT x FROM a WHERE x < 5;');
+like($res, qr/AQO mode: FROZEN/);
+
+$res = $node->safe_psql('postgres', 'EXPLAIN ANALYZE SELECT count(x) FROM a WHERE x > 5;');
+like($res, qr/AQO mode: FROZEN/);
+
+$mode = $node->safe_psql('postgres',"show aqo.mode");
+like($mode, qr/frozen/);
+
+$node->stop();
+done_testing();