diff --git a/src/handlers/utils.ts b/src/handlers/utils.ts
index 7b53af86..1aef9c81 100644
--- a/src/handlers/utils.ts
+++ b/src/handlers/utils.ts
@@ -7,6 +7,9 @@ export function VArg(argument: string) {
   if (argument === "Infinity") {
     return Infinity;
   }
+  if (argument === "undefined") {
+    return undefined;
+  }
   try {
     const val = JSON.parse(argument);
     const t = typeof val;
@@ -16,6 +19,7 @@ export function VArg(argument: string) {
   } catch {
     // ignore parsing errors
   }
+  return argument;
 }
 
 export function parseArgs(
diff --git a/test/handlers/utils.test.ts b/test/handlers/utils.test.ts
index 86266272..a6e1c157 100644
--- a/test/handlers/utils.test.ts
+++ b/test/handlers/utils.test.ts
@@ -14,6 +14,9 @@ describe("utils", () => {
     expect(VArg("null")).toBe(null);
     expect(VArg("undefined")).toBe(undefined);
     expect(VArg("Infinity")).toBe(Infinity);
+    expect(VArg("450x300")).toBe("450x300");
+    expect(VArg("cover")).toBe("cover");
+    expect(VArg("ff0000")).toBe("ff0000");
   });
 
   it("parseArgs", () => {