diff --git a/components/filesystem.rst b/components/filesystem.rst
index 2efc4cffb2e..b2799d7b922 100644
--- a/components/filesystem.rst
+++ b/components/filesystem.rst
@@ -64,6 +64,10 @@ On POSIX filesystems, directories are created with a default mode value
     You can pass an array or any :phpclass:`Traversable` object as the first
     argument.
 
+.. note::
+
+    This function ignores already existing directories.
+
 exists
 ~~~~~~