diff --git a/phpBB/download/file.php b/phpBB/download/file.php
index 1616448c0b..830967c213 100644
--- a/phpBB/download/file.php
+++ b/phpBB/download/file.php
@@ -456,6 +456,10 @@ function send_file_to_browser($attachment, $upload_dir, $category)
 	{
 		header("Content-Length: $size");
 	}
+
+	// Close the db connection before sending the file
+	$db->sql_close();
+
 	if (!set_modified_headers($attachment['filetime'], $user->browser))
 	{
 		// Try to deliver in chunks
diff --git a/phpBB/includes/db/dbal.php b/phpBB/includes/db/dbal.php
index b88873df46..af5dfa059b 100644
--- a/phpBB/includes/db/dbal.php
+++ b/phpBB/includes/db/dbal.php
@@ -147,7 +147,13 @@ class dbal
 			$this->sql_freeresult($query_id);
 		}
 
-		return $this->_sql_close();
+		// Connection closed correctly. Set db_connect_id to false to prevent errors
+		if (($result = $this->_sql_close()))
+		{
+			$this->db_connect_id = false;
+		}
+
+		return $result;
 	}
 
 	/**