diff --git a/man/subgid.5.xml b/man/subgid.5.xml
index 27799ba9..ffdb7d80 100644
--- a/man/subgid.5.xml
+++ b/man/subgid.5.xml
@@ -77,6 +77,13 @@
       Multiple ranges may be specified per user.
     </para>
 
+    <para>
+      When large number of entries (10000-100000 or more) are defined in
+      <filename>/etc/subgid</filename>, parsing performance penalty will
+      become noticeable. In this case it is recommended to use UIDs
+      instead of login names. Benchmarks have shown speed-ups up to 20x.
+    </para>
+
   </refsect1>
 
   <refsect1 id='files'>
diff --git a/man/subuid.5.xml b/man/subuid.5.xml
index 939ea166..2890661d 100644
--- a/man/subuid.5.xml
+++ b/man/subuid.5.xml
@@ -77,6 +77,13 @@
       Multiple ranges may be specified per user.
     </para>
 
+    <para>
+      When large number of entries (10000-100000 or more) are defined in
+      <filename>/etc/subuid</filename>, parsing performance penalty will
+      become noticeable. In this case it is recommended to use UIDs
+      instead of login names. Benchmarks have shown speed-ups up to 20x.
+    </para>
+
   </refsect1>
 
   <refsect1 id='files'>