diff --git a/reference/array/functions/array-unique.xml b/reference/array/functions/array-unique.xml
index 88a79d128721..ff52b00eb520 100644
--- a/reference/array/functions/array-unique.xml
+++ b/reference/array/functions/array-unique.xml
@@ -54,8 +54,17 @@
        Comparison type flags:
        <itemizedlist>
         <listitem>
-         <simpara><constant>SORT_REGULAR</constant> - compare items normally
-         (don't change types)</simpara>
+         <para>
+          <constant>SORT_REGULAR</constant> - compare items normally
+          (don't change types)
+           <note>
+            <simpara>
+             Be careful when using this flag in combination with numeric strings
+             as array values since this causes them to not be filtered out
+             correctly and you end up with duplicated values.
+            </simpara>
+           </note>
+         </para>
         </listitem>
         <listitem>
          <simpara><constant>SORT_NUMERIC</constant> - compare items numerically</simpara>