diff --git a/bin/pt-online-schema-change b/bin/pt-online-schema-change
index 63a44a47..4b500b5a 100755
--- a/bin/pt-online-schema-change
+++ b/bin/pt-online-schema-change
@@ -11134,7 +11134,7 @@ sub rebuild_constraints {
          if ($fk =~ /^__/) {
            ($new_fk = $fk) =~ s/^__//;
          } else {
-           $new_fk = '_'.$fk;
+           $new_fk = '___'.$fk;
          }
 
          PTDEBUG && _d("Old FK name: $fk New FK name: $new_fk");
diff --git a/t/pt-online-schema-change/rename_self_ref_fk_constraints.t b/t/pt-online-schema-change/rename_self_ref_fk_constraints.t
index e402e281..ce1b421b 100644
--- a/t/pt-online-schema-change/rename_self_ref_fk_constraints.t
+++ b/t/pt-online-schema-change/rename_self_ref_fk_constraints.t
@@ -32,7 +32,6 @@ my $master_dsn = 'h=127.1,P=12345,u=msandbox,p=msandbox';
 my @args       = (qw(--set-vars innodb_lock_wait_timeout=3 --alter-foreign-keys-method rebuild_constraints));
 my $output;
 my $exit_status;
-my $sample  = "t/pt-online-schema-change/samples/";
 
 # ############################################################################
 # https://bugs.launchpad.net/percona-toolkit/+bug/1632522
@@ -40,7 +39,7 @@ my $sample  = "t/pt-online-schema-change/samples/";
 # ############################################################################
 
 diag("Before loading sql");
-$sb->load_file('master', "$sample/bug-1632522.sql");
+$sb->load_file('master', "t/pt-online-schema-change/samples/bug-1632522.sql");
 diag("after loading sql");
 
 # run once: we expect the constraint name to be appended with one underscore
@@ -52,7 +51,15 @@ diag("after loading sql");
       qw(--execute)) },
 );
 
-my $constraints = $master_dbh->selectall_arrayref("SELECT TABLE_NAME, CONSTRAINT_NAME FROM information_schema.KEY_COLUMN_USAGE WHERE table_schema='bug1632522' and (TABLE_NAME='test_table' OR TABLE_NAME='person') and CONSTRAINT_NAME LIKE '%fk_%' ORDER BY TABLE_NAME, CONSTRAINT_NAME"); 
+my $query = <<"END";
+  SELECT TABLE_NAME, CONSTRAINT_NAME 
+    FROM information_schema.KEY_COLUMN_USAGE 
+   WHERE table_schema='bug1632522' 
+     AND (TABLE_NAME='test_table' OR TABLE_NAME='person') 
+     AND CONSTRAINT_NAME LIKE '%fk_%' 
+ORDER BY TABLE_NAME, CONSTRAINT_NAME
+END
+my $constraints = $master_dbh->selectall_arrayref($query);
 
 is_deeply(
    $constraints,
@@ -73,7 +80,15 @@ is_deeply(
       qw(--execute)) },
 );
 
-$constraints = $master_dbh->selectall_arrayref("SELECT TABLE_NAME, CONSTRAINT_NAME FROM information_schema.KEY_COLUMN_USAGE WHERE table_schema='bug1632522' and (TABLE_NAME='test_table' OR TABLE_NAME='person') and CONSTRAINT_NAME LIKE '%fk_%' ORDER BY TABLE_NAME, CONSTRAINT_NAME"); 
+$query = <<"END";
+  SELECT TABLE_NAME, CONSTRAINT_NAME 
+    FROM information_schema.KEY_COLUMN_USAGE 
+   WHERE table_schema='bug1632522' 
+     AND (TABLE_NAME='test_table' OR TABLE_NAME='person') 
+     AND CONSTRAINT_NAME LIKE '%fk_%' 
+ORDER BY TABLE_NAME, CONSTRAINT_NAME
+END
+$constraints = $master_dbh->selectall_arrayref($query);
 
 
 is_deeply(
@@ -94,7 +109,15 @@ is_deeply(
       qw(--execute)) },
 );
 
-$constraints = $master_dbh->selectall_arrayref("SELECT TABLE_NAME, CONSTRAINT_NAME FROM information_schema.KEY_COLUMN_USAGE WHERE table_schema='bug1632522' and (TABLE_NAME='test_table' OR TABLE_NAME='person') and CONSTRAINT_NAME LIKE '%fk_%' ORDER BY TABLE_NAME, CONSTRAINT_NAME"); 
+$query = <<"END";
+  SELECT TABLE_NAME, CONSTRAINT_NAME 
+    FROM information_schema.KEY_COLUMN_USAGE 
+   WHERE table_schema='bug1632522' 
+     and (TABLE_NAME='test_table' OR TABLE_NAME='person') 
+     and CONSTRAINT_NAME LIKE '%fk_%' 
+ORDER BY TABLE_NAME, CONSTRAINT_NAME
+END
+$constraints = $master_dbh->selectall_arrayref($query);
 
 
 is_deeply(
diff --git a/t/pt-online-schema-change/rename_self_ref_fk_constraints_pt_1802.t b/t/pt-online-schema-change/rename_self_ref_fk_constraints_pt_1802.t
new file mode 100644
index 00000000..ce1b421b
--- /dev/null
+++ b/t/pt-online-schema-change/rename_self_ref_fk_constraints_pt_1802.t
@@ -0,0 +1,138 @@
+#!/usr/bin/env perl
+
+BEGIN {
+   die "The PERCONA_TOOLKIT_BRANCH environment variable is not set.\n"
+      unless $ENV{PERCONA_TOOLKIT_BRANCH} && -d $ENV{PERCONA_TOOLKIT_BRANCH};
+   unshift @INC, "$ENV{PERCONA_TOOLKIT_BRANCH}/lib";
+};
+
+use strict;
+use warnings FATAL => 'all';
+use English qw(-no_match_vars);
+use Test::More;
+
+use Data::Dumper;
+use PerconaTest;
+use Sandbox;
+
+require "$trunk/bin/pt-online-schema-change";
+
+my $dp = new DSNParser(opts=>$dsn_opts);
+my $sb = new Sandbox(basedir => '/tmp', DSNParser => $dp);
+my $master_dbh = $sb->get_dbh_for('master');
+
+if ( !$master_dbh ) {
+   plan skip_all => 'Cannot connect to sandbox master';
+}
+
+# The sandbox servers run with lock_wait_timeout=3 and it's not dynamic
+# so we need to specify --set-vars innodb_lock_wait_timeout-3 else the
+# tool will die.
+my $master_dsn = 'h=127.1,P=12345,u=msandbox,p=msandbox';
+my @args       = (qw(--set-vars innodb_lock_wait_timeout=3 --alter-foreign-keys-method rebuild_constraints));
+my $output;
+my $exit_status;
+
+# ############################################################################
+# https://bugs.launchpad.net/percona-toolkit/+bug/1632522
+# pt-online-schema-change fails with duplicate key in table for self-referencing FK
+# ############################################################################
+
+diag("Before loading sql");
+$sb->load_file('master', "t/pt-online-schema-change/samples/bug-1632522.sql");
+diag("after loading sql");
+
+# run once: we expect the constraint name to be appended with one underscore
+# but the self-referencing constraint will have 2 underscore
+($output, $exit_status) = full_output(
+   sub { pt_online_schema_change::main(@args,
+      "$master_dsn,D=bug1632522,t=test_table",
+      "--alter", "ENGINE=InnoDB",
+      qw(--execute)) },
+);
+
+my $query = <<"END";
+  SELECT TABLE_NAME, CONSTRAINT_NAME 
+    FROM information_schema.KEY_COLUMN_USAGE 
+   WHERE table_schema='bug1632522' 
+     AND (TABLE_NAME='test_table' OR TABLE_NAME='person') 
+     AND CONSTRAINT_NAME LIKE '%fk_%' 
+ORDER BY TABLE_NAME, CONSTRAINT_NAME
+END
+my $constraints = $master_dbh->selectall_arrayref($query);
+
+is_deeply(
+   $constraints,
+   [
+      ['person', '_fk_testId'],
+      ['test_table', 'fk_person'],
+      ['test_table', 'fk_refId'],
+   ],
+   "First run adds or removes underscore from constraint names, accordingly"
+);
+
+# run second time: we expect constraint names to be prefixed with one underscore
+# if they havre't one, and to remove 2 if they have 2
+($output, $exit_status) = full_output(
+   sub { pt_online_schema_change::main(@args,
+      "$master_dsn,D=bug1632522,t=test_table",
+      "--alter", "ENGINE=InnoDB",
+      qw(--execute)) },
+);
+
+$query = <<"END";
+  SELECT TABLE_NAME, CONSTRAINT_NAME 
+    FROM information_schema.KEY_COLUMN_USAGE 
+   WHERE table_schema='bug1632522' 
+     AND (TABLE_NAME='test_table' OR TABLE_NAME='person') 
+     AND CONSTRAINT_NAME LIKE '%fk_%' 
+ORDER BY TABLE_NAME, CONSTRAINT_NAME
+END
+$constraints = $master_dbh->selectall_arrayref($query);
+
+
+is_deeply(
+   $constraints,
+   [
+      ['person', '_fk_testId'],
+      ['test_table', 'fk_person'],
+      ['test_table', 'fk_refId'],
+   ],
+   "Second run self-referencing will be one due to rebuild_constraints"
+);
+
+# run third time: we expect constraints to be the same as we started (toggled back)
+($output, $exit_status) = full_output(
+   sub { pt_online_schema_change::main(@args,
+      "$master_dsn,D=bug1632522,t=test_table",
+      "--alter", "ENGINE=InnoDB",
+      qw(--execute)) },
+);
+
+$query = <<"END";
+  SELECT TABLE_NAME, CONSTRAINT_NAME 
+    FROM information_schema.KEY_COLUMN_USAGE 
+   WHERE table_schema='bug1632522' 
+     and (TABLE_NAME='test_table' OR TABLE_NAME='person') 
+     and CONSTRAINT_NAME LIKE '%fk_%' 
+ORDER BY TABLE_NAME, CONSTRAINT_NAME
+END
+$constraints = $master_dbh->selectall_arrayref($query);
+
+
+is_deeply(
+   $constraints,
+   [
+      ['person', '_fk_testId'],
+      ['test_table', 'fk_person'],
+      ['test_table', 'fk_refId'],
+   ],
+   "Third run toggles constraint names back to how they were"
+);
+
+# #############################################################################
+# Done.
+# #############################################################################
+$sb->wipe_clean($master_dbh);
+ok($sb->ok(), "Sandbox servers") or BAIL_OUT(__FILE__ . " broke the sandbox");
+done_testing;
diff --git a/t/pt-online-schema-change/samples/pt-1802.sql b/t/pt-online-schema-change/samples/pt-1802.sql
new file mode 100644
index 00000000..4d8a0825
--- /dev/null
+++ b/t/pt-online-schema-change/samples/pt-1802.sql
@@ -0,0 +1,9 @@
+CREATE TABLE `joinit` (
+`i` int(11) NOT NULL AUTO_INCREMENT,
+`s` varchar(64) DEFAULT NULL,
+`t` time NOT NULL,
+`g` int(11) NOT NULL,
+`j` int(11) NOT NULL DEFAULT 1,
+PRIMARY KEY (`i`))
+ENGINE=InnoDB;
+ALTER TABLE joinit ADD FOREIGN KEY i_fk (j) REFERENCES joinit (i) ON UPDATE cascade ON DELETE restrict;