diff --git a/vocabularies/Org.OData.Core.V1.json b/vocabularies/Org.OData.Core.V1.json
index 2d000672..9c2078b0 100644
--- a/vocabularies/Org.OData.Core.V1.json
+++ b/vocabularies/Org.OData.Core.V1.json
@@ -630,6 +630,7 @@
                 "@Core.Description": "A path expression resolving to a primitive property of the entity type itself or to a primitive property of a complex or navigation property (recursively) of the entity type. The names of the properties in the path are joined together by forward slashes."
             },
             "Alias": {
+                "$Nullable": true,
                 "@Core.Description": "A SimpleIdentifier that MUST be unique within the set of aliases, structural and navigation properties of the containing entity type that MUST be used in the key predicate of URLs"
             }
         },
diff --git a/vocabularies/Org.OData.Core.V1.md b/vocabularies/Org.OData.Core.V1.md
index d7391d8c..1f83dab4 100644
--- a/vocabularies/Org.OData.Core.V1.md
+++ b/vocabularies/Org.OData.Core.V1.md
@@ -283,7 +283,7 @@ Property|Type|Description
 Property|Type|Description
 :-------|:---|:----------
 [Name](Org.OData.Core.V1.xml#L488)|PropertyPath|A path expression resolving to a primitive property of the entity type itself or to a primitive property of a complex or navigation property (recursively) of the entity type. The names of the properties in the path are joined together by forward slashes.
-[Alias](Org.OData.Core.V1.xml#L491)|String|A SimpleIdentifier that MUST be unique within the set of aliases, structural and navigation properties of the containing entity type that MUST be used in the key predicate of URLs
+[Alias](Org.OData.Core.V1.xml#L491)|String?|A SimpleIdentifier that MUST be unique within the set of aliases, structural and navigation properties of the containing entity type that MUST be used in the key predicate of URLs
 
 <a name="Dictionary"></a>
 ## [Dictionary](Org.OData.Core.V1.xml#L496)
diff --git a/vocabularies/Org.OData.Core.V1.xml b/vocabularies/Org.OData.Core.V1.xml
index 601a6e78..086bde89 100644
--- a/vocabularies/Org.OData.Core.V1.xml
+++ b/vocabularies/Org.OData.Core.V1.xml
@@ -488,7 +488,7 @@
         <Property Type="Edm.PropertyPath" Name="Name" Nullable="false">
           <Annotation Term="Core.Description" String="A path expression resolving to a primitive property of the entity type itself or to a primitive property of a complex or navigation property (recursively) of the entity type. The names of the properties in the path are joined together by forward slashes." />
         </Property>
-        <Property Type="Edm.String" Name="Alias" Nullable="false">
+        <Property Type="Edm.String" Name="Alias" Nullable="true">
           <Annotation Term="Core.Description" String="A SimpleIdentifier that MUST be unique within the set of aliases, structural and navigation properties of the containing entity type that MUST be used in the key predicate of URLs" />
         </Property>
       </ComplexType>