diff --git a/mdx/_rules/check_aggregate.xsl b/mdx/_rules/check_aggregate.xsl
deleted file mode 100644
index 44337a7..0000000
--- a/mdx/_rules/check_aggregate.xsl
+++ /dev/null
@@ -1,45 +0,0 @@
-<?xml version="1.0" encoding="UTF-8"?>
-<!--
-
-    check_aggregate.xsl
-
-    Checking ruleset containing aggregate-level checks.
-
-    Author: Ian A. Young <ian@iay.org.uk>
-
--->
-<xsl:stylesheet version="1.0"
-    xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
-    xmlns:md="urn:oasis:names:tc:SAML:2.0:metadata"
-    xmlns:set="http://exslt.org/sets"
-    xmlns="urn:oasis:names:tc:SAML:2.0:metadata">
-
-    <!--
-        Common support functions.
-    -->
-    <xsl:import href="check_framework.xsl"/>
-
-    <xsl:variable name="entities" select="//md:EntityDescriptor"/>
-    <xsl:variable name="idps" select="$entities[md:IDPSSODescriptor]"/>
-
-    <!--
-        Checks across the whole of the document are defined here.
-    -->
-    <xsl:template match="/">
-
-        <!-- check for duplicate entityID values -->
-        <xsl:variable name="distinct.entityIDs" select="set:distinct($entities/@entityID)"/>
-        <xsl:variable name="dup.entityIDs"
-            select="set:distinct(set:difference($entities/@entityID, $distinct.entityIDs))"/>
-        <xsl:for-each select="$dup.entityIDs">
-            <xsl:variable name="dup.entityID" select="."/>
-            <xsl:for-each select="$entities[@entityID = $dup.entityID]">
-                <xsl:call-template name="error">
-                    <xsl:with-param name="m">duplicate entityID: <xsl:value-of select='$dup.entityID'/></xsl:with-param>
-                </xsl:call-template>
-            </xsl:for-each>
-        </xsl:for-each>
-
-    </xsl:template>
-
-</xsl:stylesheet>
diff --git a/mdx/validation-beans.xml b/mdx/validation-beans.xml
index cd64cd7..5965514 100644
--- a/mdx/validation-beans.xml
+++ b/mdx/validation-beans.xml
@@ -399,8 +399,7 @@
 
         It is assumed that the entities are wrapped in a single EntitiesDescriptor.
     -->
-    <bean id="check_aggregate" parent="mda.XSLValidationStage"
-        p:XSLResource="classpath:_rules/check_aggregate.xsl"/>
+    <bean id="check_aggregate" parent="mda.DuplicateEntityInAggregateCheckingStage"/>
 
     <!--
         check_dup_display