diff --git a/src/PathComparator.php b/src/PathComparator.php
index fc0d791..4e99083 100644
--- a/src/PathComparator.php
+++ b/src/PathComparator.php
@@ -27,13 +27,13 @@ public function getCommondBase() {
             foreach($this->directories as $dir) {
                 $result = substr($dir, 0, $this->commonPrefix($result, $dir));
             }
-            return rtrim($result,'/');
+            return rtrim($result, '/');
         }
 
 
         private function commonPrefix( $s1, $s2, $i=0 ) {
             return (
-                !empty($s1[$i]) && !empty($s2[$i]) && $s1[$i] == $s2[$i]
+                $i<strlen($s1) && $i<strlen($s2) && $s1[$i] == $s2[$i]
             ) ? $this->commonPrefix( $s1, $s2, ++$i ) : $i;
         }
     }
diff --git a/tests/PathComparator.test.php b/tests/PathComparator.test.php
index 4d4f15b..ab25108 100644
--- a/tests/PathComparator.test.php
+++ b/tests/PathComparator.test.php
@@ -27,6 +27,9 @@ public function directoriesProvider() {
                 ],
                 'partns' => [
                     array(__DIR__ . '/../src', __DIR__ . '/../vendor/theseer'), dirname(__DIR__)
+                ],
+                'with0' => [
+                    [$a=__DIR__.'/_data/parser/trait0.php'], $a
                 ]
             ];
         }