diff --git a/reference/filesystem/functions/popen.xml b/reference/filesystem/functions/popen.xml
index c2b7277ed0..eb51722bd8 100644
--- a/reference/filesystem/functions/popen.xml
+++ b/reference/filesystem/functions/popen.xml
@@ -35,7 +35,14 @@
      <term><parameter>mode</parameter></term>
      <listitem>
       <para>
-       The mode
+       The mode. Either <literal>'r'</literal> for reading, or <literal>'w'</literal>
+       for writing.
+      </para>
+      <para>
+       On Windows, <function>popen</function> defaults to text mode, i.e. any <literal>\n</literal>
+       characters written to or read from the pipe will be translated to <literal>\r\n</literal>.
+       If this is not desired, binaray mode can be enforced by setting <parameter>mode</parameter>
+       to <literal>'rb'</literal> and <literal>'wb'</literal>, respectively.
       </para>
      </listitem>
     </varlistentry>