diff --git a/scripts/test-env-mutation-report.ts b/scripts/test-env-mutation-report.ts
index 9a80ec709e0c..1dcfc56f73d0 100644
--- a/scripts/test-env-mutation-report.ts
+++ b/scripts/test-env-mutation-report.ts
@@ -403,7 +403,7 @@ function parseArgs(argv: string[]): {
     }
     if (arg === "--repo-root") {
       const value = argv[index + 1];
-      if (!value || value.startsWith("--")) {
+      if (!value || value.startsWith("-")) {
         throw new Error("--repo-root expects a path");
       }
       repoRoot = value;
diff --git a/test/scripts/test-env-mutation-report.test.ts b/test/scripts/test-env-mutation-report.test.ts
index 6da083a72e78..9b0ad5307e61 100644
--- a/test/scripts/test-env-mutation-report.test.ts
+++ b/test/scripts/test-env-mutation-report.test.ts
@@ -163,24 +163,26 @@ describe("collectTestEnvMutationReport", () => {
     expect(result.stderr).toBe("");
   });
 
-  it("rejects missing CLI repo roots instead of scanning zero files", () => {
-    const result = spawnSync(
-      process.execPath,
-      [
-        "--import",
-        "tsx",
-        path.join(process.cwd(), "scripts/test-env-mutation-report.ts"),
-        "--",
-        "--repo-root",
-        "--json",
-      ],
-      {
-        encoding: "utf8",
-      },
-    );
+  it("rejects missing or flag-shaped CLI repo roots instead of scanning zero files", () => {
+    for (const value of ["--json", "-h"]) {
+      const result = spawnSync(
+        process.execPath,
+        [
+          "--import",
+          "tsx",
+          path.join(process.cwd(), "scripts/test-env-mutation-report.ts"),
+          "--",
+          "--repo-root",
+          value,
+        ],
+        {
+          encoding: "utf8",
+        },
+      );
 
-    expect(result.status).toBe(1);
-    expect(result.stderr).toContain("--repo-root expects a path");
+      expect(result.status).toBe(1);
+      expect(result.stderr).toContain("--repo-root expects a path");
+    }
   });
 
   it("rejects loose CLI limits before scanning the repository", () => {