diff --git a/mdx/_rules/check_mdrpi.xsl b/mdx/_rules/check_mdrpi.xsl
index 0588f005..76ab715f 100644
--- a/mdx/_rules/check_mdrpi.xsl
+++ b/mdx/_rules/check_mdrpi.xsl
@@ -69,6 +69,21 @@
 		</xsl:call-template>        
 	</xsl:template>
 	
+	<!--
+		Section 2.1.1
+		
+		registrationInstant values MUST be expressed in the UTC timezone using the 'Z' timezone identifier.
+	-->
+	<xsl:template match="mdrpi:RegistrationInfo[@registrationInstant]
+		[substring(@registrationInstant, string-length(@registrationInstant)) != 'Z']">
+		<xsl:call-template name="error">
+			<xsl:with-param name="m">
+				<xsl:text>registrationInstant does not end with 'Z': </xsl:text>
+				<xsl:value-of select="@registrationInstant"/>
+			</xsl:with-param>
+		</xsl:call-template>        
+	</xsl:template>
+	
 	<!--
 		Section 2.1.1