diff --git a/cliv2/cmd/cliv2/behavior/legacy/validation.go b/cliv2/cmd/cliv2/behavior/legacy/validation.go
index 25de0ced10..705ca3572a 100644
--- a/cliv2/cmd/cliv2/behavior/legacy/validation.go
+++ b/cliv2/cmd/cliv2/behavior/legacy/validation.go
@@ -100,10 +100,9 @@ func unknownCommandError(details string) error {
 
 // SetupTestMonitorCommand configures command for test/monitor to ensure parity with legacy behavior
 func SetupTestMonitorCommand(cmd *cobra.Command) {
-	// Relax flag validation for backwards compatibility by suppressing cobra's default error
-	cmd.SetFlagErrorFunc(func(_ *cobra.Command, _ error) error {
-		return unknownCommandError("")
-	})
+	// Disable flag parsing for test/monitor so that cli-extension-os-flows
+	// can manually route to the legacy CLI and handle flag validation.
+	cmd.DisableFlagParsing = true
 
 	cmd.PreRunE = func(c *cobra.Command, args []string) error {
 		if err := validateFlagsCompatibilityWithLegacy(os.Args[1:]); err != nil {
diff --git a/test/jest/acceptance/snyk-test/reachability-user-journey.spec.ts b/test/jest/acceptance/snyk-test/reachability-user-journey.spec.ts
index a56c2b2957..850d4dfd05 100644
--- a/test/jest/acceptance/snyk-test/reachability-user-journey.spec.ts
+++ b/test/jest/acceptance/snyk-test/reachability-user-journey.spec.ts
@@ -129,6 +129,29 @@ describe('snyk test --reachability', () => {
     expect(code).toBe(EXIT_CODES.VULNS_FOUND);
   });
 
+  test('emits a valid json output when unknown flags are passed', async () => {
+    const { stdout, stderr } = await runSnykCLI(
+      `test ${TEMP_LOCAL_PATH} --reachability --json --foo-bar`,
+      {
+        env: {
+          ...process.env,
+          ...ReachabilityIntegrationEnv.env,
+        },
+      },
+    );
+
+    expect(stdout).not.toBe('');
+    expect(stderr).toBe('');
+
+    const jsonOutput = JSON.parse(stdout);
+
+    const allVulnsHaveReachabilitySignal = jsonOutput.vulnerabilities.every(
+      (vuln: { reachability: string }) => !!vuln.reachability,
+    );
+
+    expect(allVulnsHaveReachabilitySignal).toBeTruthy();
+  });
+
   test('emits a valid json output and fails the test if vulnerabilies are upgradable', async () => {
     const { stdout, code, stderr } = await runSnykCLI(
       `test ${TEMP_LOCAL_PATH} --reachability --fail-on=upgradable --json`,