diff --git a/reference/session/functions/session-gc.xml b/reference/session/functions/session-gc.xml
index 0f12d0b08d39..9bdbb80e2434 100644
--- a/reference/session/functions/session-gc.xml
+++ b/reference/session/functions/session-gc.xml
@@ -30,6 +30,15 @@
    <link linkend="ini.session.gc-probability">session.gc_probability</link> 
    to 0.
   </para>
+  <note>
+   <para>
+    For <function>session_gc</function> to work correctly, the
+    <link linkend="ini.session.save-path">session.save_path</link> must be set
+    to the same value as web requests and the script must have access and
+    permissions for the same files. This may be affected by the user the script
+    runs as and container / sandboxing features such as systemd's <literal>PrivateTmp=</literal> option.
+   </para>
+  </note>
  </refsect1>
 
  <refsect1 role="parameters">