diff --git a/phpBB/includes/acp/acp_board.php b/phpBB/includes/acp/acp_board.php
index d537885ef1..ce2ddc3b0b 100644
--- a/phpBB/includes/acp/acp_board.php
+++ b/phpBB/includes/acp/acp_board.php
@@ -906,11 +906,13 @@ class acp_board
 		global $user, $config;
 
 		// Let the format_date function operate with the acp values
-		$old_tz = $user->timezone;
-		$old_dst = $user->dst;
-
-		$user->timezone = $config['board_timezone'] * 3600;
-		$user->dst = $config['board_dst'] * 3600;
+		$old_tz = $user->tz;
+		if (is_numeric($config['board_timezone']))
+		{
+			// Might still be numeric by chance
+			$config['board_timezone'] = sprintf('Etc/GMT%+d', $config['board_timezone']);
+		}
+		$user->tz = new DateTimeZone($config['board_timezone']);
 
 		$dateformat_options = '';
 
@@ -929,8 +931,7 @@ class acp_board
 		$dateformat_options .= '>' . $user->lang['CUSTOM_DATEFORMAT'] . '</option>';
 
 		// Reset users date options
-		$user->timezone = $old_tz;
-		$user->dst = $old_dst;
+		$user->tz = $old_tz;
 
 		return "<select name=\"dateoptions\" id=\"dateoptions\" onchange=\"if (this.value == 'custom') { document.getElementById('" . addslashes($key) . "').value = '" . addslashes($value) . "'; } else { document.getElementById('" . addslashes($key) . "').value = this.value; }\">$dateformat_options</select>
 		<input type=\"text\" name=\"config[$key]\" id=\"$key\" value=\"$value\" maxlength=\"30\" />";