diff --git a/scripts/bench-gateway-startup.ts b/scripts/bench-gateway-startup.ts
index 79e61f3ac52..56fbea9fefe 100644
--- a/scripts/bench-gateway-startup.ts
+++ b/scripts/bench-gateway-startup.ts
@@ -206,12 +206,19 @@ function readRequiredFlagValue(argv: string[], index: number, flag: string): str
 }
 
 function validateCliArgs(argv: string[]): void {
+  const seenSingleValueFlags = new Set<string>();
   for (let index = 0; index < argv.length; index += 1) {
     const arg = argv[index] ?? "";
     if (BOOLEAN_FLAGS.has(arg)) {
       continue;
     }
     if (VALUE_FLAGS.has(arg)) {
+      if (arg !== "--case") {
+        if (seenSingleValueFlags.has(arg)) {
+          throw new CliArgumentError(`${arg} was provided more than once`);
+        }
+        seenSingleValueFlags.add(arg);
+      }
       readRequiredFlagValue(argv, index, arg);
       index += 1;
       continue;
diff --git a/test/scripts/bench-gateway-startup.test.ts b/test/scripts/bench-gateway-startup.test.ts
index f248a518888..d451d14443e 100644
--- a/test/scripts/bench-gateway-startup.test.ts
+++ b/test/scripts/bench-gateway-startup.test.ts
@@ -84,6 +84,9 @@ describe("gateway startup benchmark script", () => {
     expect(() => testing.parseOptions(["--case", "default", "--case", "default"])).toThrow(
       'Duplicate --case "default"',
     );
+    expect(() =>
+      testing.parseOptions(["--output", "first.json", "--output", "second.json"]),
+    ).toThrow("--output was provided more than once");
     expect(() => testing.resolveEntry("--inspect")).toThrow(/must be a file path/u);
   });