diff --git a/lib/internal/Magento/Framework/View/Layout/etc/elements.xsd b/lib/internal/Magento/Framework/View/Layout/etc/elements.xsd
index ea80380865e6a..39cdec05a65ea 100755
--- a/lib/internal/Magento/Framework/View/Layout/etc/elements.xsd
+++ b/lib/internal/Magento/Framework/View/Layout/etc/elements.xsd
@@ -138,7 +138,7 @@
 
     <xs:simpleType name="blockClassType">
         <xs:restriction base="xs:string">
-            <xs:pattern value="[A-Z][a-zA-Z\d]*(\\[A-Z][a-zA-Z\d]*)*"/>
+            <xs:pattern value="[A-Z][_a-zA-Z\d]*(\\[A-Z][_a-zA-Z\d]*)*"/>
         </xs:restriction>
     </xs:simpleType>