diff --git a/lib/ClassMap.php b/lib/ClassMap.php
index b094d7432..ca7b26a20 100644
--- a/lib/ClassMap.php
+++ b/lib/ClassMap.php
@@ -189,7 +189,7 @@ protected function filterDuplicates(array $map, $mapName)
                 $map[$name] = key($classes);
                 unset($this->duplicates[$name]);
             } else {
-                $this->duplicates = $classes;
+                $this->duplicates[$name] = $classes;
             }
         }