diff --git a/phpBB/feed.php b/phpBB/feed.php
index 8971bae768..d4dfb15928 100644
--- a/phpBB/feed.php
+++ b/phpBB/feed.php
@@ -164,7 +164,7 @@ if (defined('DEBUG') && request_var('explain', 0) && $auth->acl_get('a_'))
 {
 	header('Content-type: text/html; charset=UTF-8');
 	header('Cache-Control: private, no-cache="set-cookie"');
-	header('Expires: 0');
+	header('Expires: ' . gmdate('D, d M Y H:i:s', time()) . ' GMT');
 	header('Pragma: no-cache');
 
 	$mtime = explode(' ', microtime());
diff --git a/phpBB/includes/functions.php b/phpBB/includes/functions.php
index 7dfaea6f48..a61518401c 100644
--- a/phpBB/includes/functions.php
+++ b/phpBB/includes/functions.php
@@ -5062,7 +5062,7 @@ function page_header($page_title = '', $display_online_list = false, $item_id =
 		// application/xhtml+xml not used because of IE
 		'Content-type' => 'text/html; charset=UTF-8',
 		'Cache-Control' => 'private, no-cache="set-cookie"',
-		'Expires' => '0',
+		'Expires' => gmdate('D, d M Y H:i:s', time()) . ' GMT',
 		'Pragma' => 'no-cache',
 	);
 	if (!empty($user->data['is_bot']))
diff --git a/phpBB/includes/functions_acp.php b/phpBB/includes/functions_acp.php
index d9dc11239c..da8d756db9 100644
--- a/phpBB/includes/functions_acp.php
+++ b/phpBB/includes/functions_acp.php
@@ -112,7 +112,7 @@ function adm_page_header($page_title)
 		// application/xhtml+xml not used because of IE
 		'Content-type' => 'text/html; charset=UTF-8',
 		'Cache-Control' => 'private, no-cache="set-cookie"',
-		'Expires' => '0',
+		'Expires' => gmdate('D, d M Y H:i:s', time()) . ' GMT',
 		'Pragma' => 'no-cache',
 	);
 
diff --git a/phpBB/includes/functions_download.php b/phpBB/includes/functions_download.php
index 4ff3994f4c..3be84299f0 100644
--- a/phpBB/includes/functions_download.php
+++ b/phpBB/includes/functions_download.php
@@ -56,17 +56,17 @@ function send_avatar_to_browser($file, $browser)
 
 			if (strpos(strtolower($browser), 'msie 6.0') !== false)
 			{
-				header('Expires: -1');
+				header('Expires: ' . gmdate('D, d M Y H:i:s', time()) . ' GMT');
 			}
 			else
 			{
-				header('Expires: ' . gmdate('D, d M Y H:i:s \G\M\T', time() + 31536000));
+				header('Expires: ' . gmdate('D, d M Y H:i:s', time() + 31536000) . ' GMT');
 			}
 		}
 		else
 		{
 			header('Content-Disposition: inline; ' . header_filename($file));
-			header('Expires: ' . gmdate('D, d M Y H:i:s \G\M\T', time() + 31536000));
+			header('Expires: ' . gmdate('D, d M Y H:i:s', time() + 31536000) . ' GMT');
 		}
 
 		$size = @filesize($file_path);
@@ -197,7 +197,7 @@ function send_file_to_browser($attachment, $upload_dir, $category)
 			header('Content-Disposition: attachment; ' . header_filename(htmlspecialchars_decode($attachment['real_filename'])));
 			if (empty($user->browser) || (strpos(strtolower($user->browser), 'msie 6.0') !== false))
 			{
-				header('expires: -1');
+				header('Expires: ' . gmdate('D, d M Y H:i:s', time()) . ' GMT');
 			}
 		}
 		else
@@ -421,7 +421,7 @@ function set_modified_headers($stamp, $browser)
 			send_status_line(304, 'Not Modified');
 			// seems that we need those too ... browsers
 			header('Pragma: public');
-			header('Expires: ' . gmdate('D, d M Y H:i:s \G\M\T', time() + 31536000));
+			header('Expires: ' . gmdate('D, d M Y H:i:s', time() + 31536000) . ' GMT');
 			return true;
 		}
 		else
diff --git a/phpBB/install/index.php b/phpBB/install/index.php
index ccfa64796c..b7369c4b1f 100644
--- a/phpBB/install/index.php
+++ b/phpBB/install/index.php
@@ -467,7 +467,7 @@ class module
 
 		header('Content-type: text/html; charset=UTF-8');
 		header('Cache-Control: private, no-cache="set-cookie"');
-		header('Expires: 0');
+		header('Expires: ' . gmdate('D, d M Y H:i:s', time()) . ' GMT');
 		header('Pragma: no-cache');
 
 		return;