diff --git a/bin/pt-online-schema-change b/bin/pt-online-schema-change
index c46be90b..eca27849 100755
--- a/bin/pt-online-schema-change
+++ b/bin/pt-online-schema-change
@@ -10037,6 +10037,9 @@ sub check_alter {
 
    my $ok = 1;
 
+   $alter =~ s/^(.*?)\s+COMMENT\s+'(.*?[^\\]')+(.*)/$1$3/; 
+   $alter =~ s/^(.*?)\s+COMMENT\s+"(.*?[^\\]")+(.*)/$1$3/; 
+
    my $unique_fields = get_unique_index_fields($alter);
 
    if (scalar @$unique_fields && $o->get('check-unique-key-change')) {
@@ -10056,6 +10059,12 @@ sub check_alter {
         die ($msg);
    }
 
+   if ( ($tbl->{tbl_struct}->{engine} || '') =~ m/RocksDB/i ) {
+       if ($alter =~ m/FOREIGN KEY/i) {
+            my $msg = "FOREIGN KEYS are not supported by the RocksDB engine\n\n";
+            die ($msg);
+       }
+   }
    # ########################################################################
    # Check for DROP PRIMARY KEY.
    # ########################################################################
diff --git a/sandbox/start-sandbox b/sandbox/start-sandbox
index 7246df8f..f11702b2 100755
--- a/sandbox/start-sandbox
+++ b/sandbox/start-sandbox
@@ -174,6 +174,13 @@ make_sandbox() {
       /tmp/$port/use -e "start slave"
    fi
 
+   if [ -x "$PERCONA_TOOLKIT_SANDBOX/bin/ps-admin" ]; then
+       # try to enable RocksDB. Only available on Percona Server 5.7.19+
+       if [ "$version" ">" "5.6" ]; then
+           $PERCONA_TOOLKIT_SANDBOX/bin/ps-admin --enable-rocksdb -u root -pmsandbox -h 127.1 -P $port
+       fi
+   fi
+
    return 0
 }
 
diff --git a/t/lib/TableParser.t b/t/lib/TableParser.t
index 91137219..d1ca2225 100644
--- a/t/lib/TableParser.t
+++ b/t/lib/TableParser.t
@@ -1161,7 +1161,7 @@ SKIP: {
         },
         engine => 'InnoDB',
         is_autoinc => { column2 => 0, column3 => 0, id => 0 },
-        is_col => { column2 => 1, column3 => 1, id => 1 },
+        is_col => { column2 => 1, id => 1 },
         is_generated => { column3 => 1 },
         is_nullable => { column2 => 1, column3 => 1 },
         is_numeric => { column2 => 1, column3 => 1, id => 1 },
diff --git a/t/pt-online-schema-change/pt-209.t b/t/pt-online-schema-change/pt-209.t
new file mode 100644
index 00000000..72512541
--- /dev/null
+++ b/t/pt-online-schema-change/pt-209.t
@@ -0,0 +1,89 @@
+#!/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 threads;
+
+use English qw(-no_match_vars);
+use Test::More;
+
+use Data::Dumper;
+use PerconaTest;
+use Sandbox;
+use SqlModes;
+use File::Temp qw/ tempdir /;
+
+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');
+my $master_dsn = 'h=127.1,P=12345,u=msandbox,p=msandbox';
+
+if ( !$master_dbh ) {
+   plan skip_all => 'Cannot connect to sandbox master';
+}
+
+if ($sandbox_version lt '5.7') {
+   plan skip_all => "RocksDB is only available on Percona Server 5.7.19+";
+}
+
+my $rows = $master_dbh->selectall_arrayref('SHOW ENGINES', {Slice=>{}});
+my $rocksdb_enabled;
+for my $row (@$rows) {
+    if ($row->{engine} eq 'ROCKSDB') {
+        $rocksdb_enabled = 1;
+        last;
+    }
+}
+
+if (!$rocksdb_enabled) {
+   plan skip_all => "RocksDB engine is not available";
+}
+
+plan tests => 3;
+
+# 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 @args       = (qw(--set-vars innodb_lock_wait_timeout=3));
+my $output;
+my $exit_status;
+my $sample  = "t/pt-online-schema-change/samples/";
+
+$sb->load_file('master', "$sample/pt-209.sql");
+
+($output, $exit_status) = full_output(
+   sub { pt_online_schema_change::main(@args, "$master_dsn,D=test,t=t1",
+         '--execute', 
+         '--alter', "ADD CONSTRAINT fk_some_id FOREIGN KEY (some_id) REFERENCES some(id)`",
+         ),
+      },
+);
+
+isnt(
+      $exit_status,
+      0,
+      "PT-209 Altering RocksDB table adding a foreign key exit status != 0",
+);
+
+like(
+      $output,
+      qr/FOREIGN KEYS are not supported by the RocksDB engine/s,
+      "PT-209 Message cannot add FKs to a RocksDB table",
+);
+
+$master_dbh->do("DROP DATABASE IF EXISTS test");
+
+# #############################################################################
+# 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-209.sql b/t/pt-online-schema-change/samples/pt-209.sql
new file mode 100644
index 00000000..8fb44059
--- /dev/null
+++ b/t/pt-online-schema-change/samples/pt-209.sql
@@ -0,0 +1,8 @@
+CREATE SCHEMA IF NOT EXISTS test;
+USE test;
+DROP TABLE IF EXISTS t1;
+CREATE TABLE `test`.`t1` (
+`ID` int(11) NOT NULL,
+`Column2` int(11) DEFAULT NULL,
+PRIMARY KEY (`ID`)
+) ENGINE=RocksDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci;