diff --git a/reference/filesystem/functions/basename.xml b/reference/filesystem/functions/basename.xml
index 0396d4e896..6ed4f3966a 100644
--- a/reference/filesystem/functions/basename.xml
+++ b/reference/filesystem/functions/basename.xml
@@ -29,6 +29,8 @@
     <function>basename</function> is locale aware, so for it to see the 
     correct basename with multibyte character paths, the matching locale must 
     be set using the <function>setlocale</function> function.
+    If <parameter>path</parameter> contains characters which are invalid for the
+    current locale, the behavior of <function>basename</function> is undefined.
    </para>
   </caution>
  </refsect1>
diff --git a/reference/filesystem/functions/dirname.xml b/reference/filesystem/functions/dirname.xml
index d9bcfe001b..a059fce237 100644
--- a/reference/filesystem/functions/dirname.xml
+++ b/reference/filesystem/functions/dirname.xml
@@ -27,9 +27,16 @@
   </note>
   <caution>
    <para>
-    <function>dirname</function> is locale aware, so for it to see the 
-    correct directory name with multibyte character paths, the matching locale must 
-    be set using the <function>setlocale</function> function.
+    On Windows, <function>dirname</function> assumes the currently set codepage, so for it to see the 
+    correct directory name with multibyte character paths, the matching codepage must 
+    be set.
+    If <parameter>path</parameter> contains characters which are invalid for the
+    current codepage, the behavior of <function>basename</function> is undefined.
+   </para>
+   <para>
+    On other systems, <function>dirname</function> assumes <parameter>path</parameter>
+    to be encoded in an ASCII compatible encoding. Otherwise the behavior of the
+    the function is undefined.
    </para>
   </caution>
  </refsect1>