diff --git a/utils/doclint/documentation.js b/utils/doclint/documentation.js
index 7972ba507e..7340178b35 100644
--- a/utils/doclint/documentation.js
+++ b/utils/doclint/documentation.js
@@ -866,6 +866,7 @@ function csharpOptionOverloadSuffix(option, type) {
     case 'Buffer': return 'Byte';
     case 'Serializable': return 'Object';
     case 'int': return 'Int';
+    case 'long': return 'Int64';
     case 'Date': return 'Date';
   }
   throw new Error(`CSharp option "${option}" has unsupported type overload "${type}"`);
diff --git a/utils/doclint/generateDotnetApi.js b/utils/doclint/generateDotnetApi.js
index eb9e681ff1..db2204617b 100644
--- a/utils/doclint/generateDotnetApi.js
+++ b/utils/doclint/generateDotnetApi.js
@@ -829,7 +829,7 @@ function translateType(type, parent, generateNameCallback = t => t.name, optiona
  * @param {Documentation.Type} type
  */
 function registerModelType(typeName, type) {
-  if (['object', 'string', 'int'].includes(typeName))
+  if (['object', 'string', 'int', 'long'].includes(typeName))
     return;
   if (typeName.endsWith('Option'))
     return;