diff --git a/reference/filesystem/functions/fopen.xml b/reference/filesystem/functions/fopen.xml
index 6d87c5c8f7..177fc1fa9e 100644
--- a/reference/filesystem/functions/fopen.xml
+++ b/reference/filesystem/functions/fopen.xml
@@ -352,6 +352,10 @@ $handle = fopen("ftp://user:password@example.com/somefile.txt", "w");
    the files and directories you're using are accessible to the server
    process.
   </para>
+  <para>
+   This function may success for directories. Use <function>is_dir</function>
+   to distinguish file and directory.
+  </para>
  </refsect1>
 
  <refsect1 role="seealso">
diff --git a/reference/filesystem/functions/is-readable.xml b/reference/filesystem/functions/is-readable.xml
index 1e15b2c62d..17f1f37c77 100644
--- a/reference/filesystem/functions/is-readable.xml
+++ b/reference/filesystem/functions/is-readable.xml
@@ -81,6 +81,10 @@ if (is_readable($filename)) {
     The check is done using the real UID/GID instead of the effective one.
    </para>
   </note>
+  <para>
+   This function may return &true; for directories. Use
+   <function>is_dir</function> to distinguish file and directory.
+  </para>
  </refsect1>
 
  <refsect1 role="seealso">