diff --git a/sigprops.xsd b/sigprops.xsd
index 134f57257e9a938c5027994b00353a9991872d61..5dcf7a114e0d29e0c3189293c8c0cbbb2a1afeaa 100644
--- a/sigprops.xsd
+++ b/sigprops.xsd
@@ -94,7 +94,7 @@
                     <xs:documentation>Name of the significant property.</xs:documentation>
                 </xs:annotation>
             </xs:element>
-            <xs:element name="PropertyExplanation" minOccurs="0" maxOccurs="1">
+            <xs:element name="PropertyExplanation" minOccurs="1" maxOccurs="1">
                 <xs:annotation>
                     <xs:documentation>More detailed explanation of why this property is
                         significant.</xs:documentation>