diff --git a/lib/base.php b/lib/base.php
index f9818d3514e7..ab3064feeb7b 100644
--- a/lib/base.php
+++ b/lib/base.php
@@ -125,26 +125,99 @@ public static function autoload($className)
 	public static function initPaths()
 	{
 		// calculate the root directories
+
+		// Some comments because this code is a bit tricky, as requested here :
+		// https://github.com/owncloud/core/pull/385
+
+		// Imagine your httpd document root is '/var/www'
+		// -> requesting /index.html serves /var/www/index.html
+		// Imagine you have an alias named 'alias'
+		// -> requesting /alias/index.html serves /var/www/index.html
+		// Imagine you put owncloud on a subdir named 'dir'
+		// -> requesting /alias/dir/index.html serves /var/www/dir/index.html
+
+		// When requesting /alias/dir/index.php, it require lib/base.php
+		// __DIR__ == '/var/www/dir/lib'
+		//
+		// OC::$SERVERROOT=str_replace("\\", '/', substr(__DIR__, 0, -4));
+		// is similar to
+		// OC::$SERVERROOT=str_replace("\\", '/', substr(__DIR__, 0, strlen('/lib')));
+		//
+		// after that,
+		// OC::$SERVERROOT == '/var/www/dir'
+
+		// Note : I suppose that str_replace("\", '/', str) is to translate DOS path into Web path because
+		// various substr calls expects only one character as dir separator (I don't use any NT server,
+		// this part of the code was not my idea).
+
 		OC::$SERVERROOT = str_replace("\\", '/', substr(__DIR__, 0, -4));
-		OC::$SUBURI = str_replace("\\", "/", substr(realpath($_SERVER["SCRIPT_FILENAME"]), strlen(OC::$SERVERROOT)));
+
+		// In this example, $documentRoot == '/var/www'
+
+		$documentRoot = realpath($_SERVER['DOCUMENT_ROOT']);
+
+		// If requesting /alias/dir/index.php/pathinfo or /alias/dir/index.php?param
+		// Then $scriptName == '/alias/dir/index.php'
+
 		$scriptName = $_SERVER["SCRIPT_NAME"];
-		if (substr($scriptName, -1) == '/') {
-			$scriptName .= 'index.php';
-			//make sure suburi follows the same rules as scriptName
-			if (substr(OC::$SUBURI, -9) != 'index.php') {
-				if (substr(OC::$SUBURI, -1) != '/') {
-					OC::$SUBURI = OC::$SUBURI . '/';
-				}
-				OC::$SUBURI = OC::$SUBURI . 'index.php';
-			}
+
+		// If requesting /alias/dir/index.php/pathinfo or /alias/dir/index.php?param
+		// Then $scriptFileName == '/var/www/dir/index.php'
+		// realpath() function is used here because previous __DIR__ call return implicitely real path
+		// We will compare later OC::$SERVERROOT and $scriptFileName, so we should not be disturbed
+		// by symlinks in file path
+
+		$scriptFileName = realpath($_SERVER["SCRIPT_FILENAME"]);
+
+		// If requesting /alias/dir/index.php/pathinfo
+		// Then $pathInfo == '/pathinfo'
+
+		if (isset($_SERVER["PATH_INFO"])) {
+			$pathInfo = $_SERVER["PATH_INFO"];
+		}
+		else {
+			$pathInfo = "";
+		}
+		$subDir = "";
+		$alias = "";
+
+		// If '/var/www' != '/var/www/dir'
+		// Then $subDir = substr('/var/www/dir', strlen('/var/www'))
+		// Then $subDir == '/dir'
+
+		if (strcmp($documentRoot, OC::$SERVERROOT)) {
+			$subDir = substr(OC::$SERVERROOT,strlen($documentRoot));
 		}
 
-		OC::$WEBROOT = substr($scriptName, 0, strlen($scriptName) - strlen(OC::$SUBURI));
+		// If '/var/www/dir' . '/alias/index.php' != '/var/www/dir/index.php' // True
+		// Then $alias = substr('/alias/index.php', 0, strlen('/var/www/dir') - strlen('/dir') - strlen('/var/www/dir/index.php'))
+		// Then $alias = substr('/alias/index.php', 0, strlen('/var/www/dir') - strlen('/var/www/dir/index.php'))
+		// Then $alias = substr('/alias/index.php', 0, 0 - strlen('/index.php'))
+		// Then $alias == '/alias
 
-		if (OC::$WEBROOT != '' and OC::$WEBROOT[0] !== '/') {
-			OC::$WEBROOT = '/' . OC::$WEBROOT;
+		if(strcmp(OC::$SERVERROOT.$scriptName, $scriptFileName)) {
+			$alias = substr($scriptName, 0, strlen(OC::$SERVERROOT) - strlen($subDir) - strlen($scriptFileName));
 		}
 
+		// If requesting /alias/dir/index.php
+		// Then OC::$WEBROOT = '/alias' . '/dir'
+		// Then OC::$WEBROOT = '/alias/dir'
+		// Else If no alias, or no subdir
+		// Then OC::$WEBROOT = ''
+
+		OC::$WEBROOT = $alias.$subDir;
+
+		// If requesting /alias/dir/index.php/pathinfo
+		// Then OC::$SUBURI = substr('/alias/dir/index.php', 1 + strlen('/alias')).'/pathinfo'
+		// Then OC::$SUBURI = substr('/alias/dir/index.php', strlen('/alias/')).'/pathinfo'
+		// Then OC::$SUBURI = 'dir/index.php'.'/pathinfo'
+		// Then OC::$SUBURI = 'dir/index.php/pathinfo'
+		// Then OC::$SUBURI = 'dir/index.php/pathinfo'
+		// Else If no subdir
+		// OC::$SUBURI = 'index.php/pathinfo'
+
+		OC::$SUBURI = substr($scriptName, 1 + strlen($alias)).$pathInfo;
+
 		// ensure we can find OC_Config
 		set_include_path(
 			OC::$SERVERROOT . '/lib' . PATH_SEPARATOR .