diff --git a/tests/10apidoc/01register.pl b/tests/10apidoc/01register.pl
index 443784a83..abc2092fc 100644
--- a/tests/10apidoc/01register.pl
+++ b/tests/10apidoc/01register.pl
@@ -219,7 +219,7 @@ sub local_admin_fixture
       setup => sub {
          my ( $http, $localpart ) = @_;
 
-         matrix_register_user_via_secret( $http, $localpart, admin => 1, %args );
+         matrix_register_user_via_secret( $http, $localpart, is_admin => 1, %args );
       },
    );
 }
diff --git a/tests/48admin.pl b/tests/48admin.pl
index ebc905a88..9045cf92a 100644
--- a/tests/48admin.pl
+++ b/tests/48admin.pl
@@ -1,3 +1,5 @@
+use Future::Utils qw( repeat );
+
 test "/whois",
    requires => [ $main::API_CLIENTS[0] ],
 
@@ -36,3 +38,222 @@
          Future->done( 1 );
       });
    };
+
+test "/purge_history",
+   requires => [ local_admin_fixture(), local_user_and_room_fixtures() ],
+
+   do => sub {
+      my ( $admin, $user, $room_id ) = @_;
+
+      my $last_event_id;
+
+      matrix_put_room_state( $user, $room_id,
+         type    => "m.room.name",
+         content => { name => "A room name" },
+      )->then( sub {
+         matrix_sync( $user )
+      })->then( sub {
+         repeat( sub {
+            my $msgnum = $_[0];
+
+            matrix_send_room_text_message( $user, $room_id,
+               body => "Message $msgnum",
+            )
+         }, foreach => [ 1 .. 10 ])
+      })->then( sub {
+         ( $last_event_id ) = @_;
+
+         await_message_in_room( $user, $room_id, $last_event_id ),
+      })->then( sub {
+         do_request_json_for( $user,
+            method  => "POST",
+            uri     => "/r0/admin/purge_history/$room_id/$last_event_id",
+            content => {}
+         )->main::expect_http_403;  # Must be server admin
+      })->then( sub {
+         do_request_json_for( $admin,
+            method  => "POST",
+            uri     => "/r0/admin/purge_history/$room_id/$last_event_id",
+            content => {}
+         )
+      })->then( sub {
+         # Test that /sync with an existing token still works.
+         matrix_sync_again( $user )
+      })->then( sub {
+         # Test that an initial /sync has the correct data.
+         matrix_sync( $user )
+      })->then( sub {
+         my ( $body ) = @_;
+
+         assert_json_keys( $body->{rooms}{join}, $room_id );
+         my $room =  $body->{rooms}{join}{$room_id};
+
+         log_if_fail( "Room", $room->{timeline}{events} );
+
+         # The only message event should be the last one.
+         all {
+            $_->{type} ne "m.room.message" || $_->{event_id} eq $last_event_id
+         } @{ $room->{timeline}{events} } or die "Expected no message events";
+
+         # Ensure we still see the state.
+         foreach my $expected_type( qw(
+            m.room.create
+            m.room.member
+            m.room.power_levels
+            m.room.name
+         ) ) {
+            any { $_->{type} eq $expected_type } @{ $room->{state}{events} }
+               or die "Expected state event of type $expected_type";
+         }
+
+         Future->done( 1 );
+      })
+   };
+
+test "Can backfill purged history",
+   requires => [ local_admin_fixture(), local_user_and_room_fixtures(),
+                 remote_user_fixture(), qw( can_paginate_room_remotely ) ],
+
+   do => sub {
+      my ( $admin, $user, $room_id, $remote_user ) = @_;
+
+      my @event_ids;
+      my $last_event_id;
+
+      matrix_invite_user_to_room( $user, $remote_user, $room_id )
+      ->then( sub {
+         matrix_join_room( $remote_user, $room_id )
+      })->then( sub {
+         matrix_put_room_state( $user, $room_id,
+            type    => "m.room.name",
+            content => { name => "A room name" },
+         )
+      })->then( sub {
+         Future->needs_all(
+            matrix_sync( $user ),
+            matrix_sync( $remote_user )
+         )
+      })->then( sub {
+         # Send half the messages as the local user...
+         repeat( sub {
+            my $msgnum = $_[0];
+
+            matrix_send_room_text_message( $user, $room_id,
+               body => "Message $msgnum",
+            )->on_done( sub { push @event_ids, $_[0]; } )
+         }, foreach => [ 0 .. 4 ])
+      })->then( sub {
+         my ( $last_local_id ) = @_;
+
+         # Wait until both users see the last event
+         Future->needs_all(
+            await_message_in_room( $user, $room_id, $last_local_id ),
+            await_message_in_room( $remote_user, $room_id, $last_local_id )
+         )
+      })->then( sub {
+         # ... and half as the remote. This is useful to esnre that both local
+         # and remote events are handled correctly.
+         repeat( sub {
+            my $msgnum = $_[0];
+
+            matrix_send_room_text_message( $remote_user, $room_id,
+               body => "Message $msgnum",
+            )->on_done( sub { push @event_ids, $_[0]; } )
+         }, foreach => [ 5 .. 9 ])
+      })->then( sub {
+         ( $last_event_id ) = @_;
+
+         log_if_fail "last_event_id", $last_event_id;
+
+         # Wait until both users see the last event
+         Future->needs_all(
+            await_message_in_room( $user, $room_id, $last_event_id ),
+            await_message_in_room( $remote_user, $room_id, $last_event_id )
+         )
+      })->then( sub {
+         do_request_json_for( $admin,
+            method  => "POST",
+            uri     => "/r0/admin/purge_history/$room_id/$last_event_id",
+            content => {}
+         )
+      })->then( sub {
+         matrix_sync( $user )
+      })->then( sub {
+         my ( $body ) = @_;
+
+         assert_json_keys( $body->{rooms}{join}, $room_id );
+         my $room =  $body->{rooms}{join}{$room_id};
+
+         log_if_fail( "Room timeline", $room->{timeline}{events} );
+
+         # The only message event should be the last one.
+         all {
+            $_->{type} ne "m.room.message" || $_->{event_id} eq $last_event_id
+         } @{ $room->{timeline}{events} } or die "Expected no message events";
+
+         # Ensure we still see the state.
+         foreach my $expected_type( qw(
+            m.room.create
+            m.room.member
+            m.room.power_levels
+            m.room.name
+         ) ) {
+            any { $_->{type} eq $expected_type } @{ $room->{state}{events} }
+               or die "Expected state event of type $expected_type";
+         }
+
+         my $prev_batch = $room->{timeline}{prev_batch};
+
+         my @missing_event_ids = grep { $_ ne $last_event_id } @event_ids;
+
+         # Keep paginating untill we see all the old messages.
+         repeat( sub {
+            log_if_fail "prev_batch", $prev_batch;
+            matrix_get_room_messages( $user, $room_id,
+               limit => 20,
+               from => $prev_batch,
+            )->on_done( sub {
+               my ( $body ) = @_;
+
+               log_if_fail( "Pagination result", $body );
+
+               $prev_batch ne $body->{end} or die "Pagination token did not change";
+
+               $prev_batch = $body->{end};
+
+               foreach my $event ( @{ $body->{chunk} } ) {
+                  @missing_event_ids = grep {
+                     $_ ne $event->{event_id}
+                  } @missing_event_ids;
+               }
+
+               log_if_fail "Missing", \@missing_event_ids;
+            })
+         }, while => sub { scalar @missing_event_ids > 0 });
+      });
+   };
+
+
+sub await_message_in_room
+{
+   my ( $user, $room_id, $event_id ) = @_;
+
+   my $user_id = $user->user_id;
+
+   repeat( sub {
+      matrix_sync_again( $user, timeout => 500 )
+      ->then( sub {
+         my ( $body ) = @_;
+
+         log_if_fail "Sync for $user_id", $body;
+
+         Future->done( any {
+            $_->{event_id} eq $event_id
+         } @{ $body->{rooms}{join}{$room_id}{timeline}{events} } )
+      })
+   }, until => sub {
+      $_[0]->failure or $_[0]->get
+   })->on_done( sub {
+      log_if_fail "Found event $event_id for $user_id";
+   })
+}