diff --git a/types/webidl2/index.d.ts b/types/webidl2/index.d.ts
index a31fa3550e..9992642749 100644
--- a/types/webidl2/index.d.ts
+++ b/types/webidl2/index.d.ts
@@ -192,7 +192,7 @@ export interface OperationMemberType {
     /** The name of the operation. If a stringifier, may be null. */
     name: string | null;
     /** An array of arguments for the operation. */
-    arguments: Argument[] | null;
+    arguments: Argument[];
     /** A list of extended attributes. */
     extAttrs: ExtendedAttributes[];
 }