diff --git a/lib/validators/brief-validator.mjs b/lib/validators/brief-validator.mjs
index f93d2e2..7f25d90 100644
--- a/lib/validators/brief-validator.mjs
+++ b/lib/validators/brief-validator.mjs
@@ -252,7 +252,11 @@ if (import.meta.url === `file://${process.argv[1]}`) {
   const minIdx = args.indexOf('--min-version');
   const minBriefVersion = minIdx >= 0 ? args[minIdx + 1] : undefined;
   // filePath is the first positional, skipping the --min-version value token.
-  const filePath = args.find((a, i) => !a.startsWith('--') && i !== minIdx + 1);
+  // Guard: when --min-version is absent (minIdx === -1) the skip index must be -1,
+  // not 0 — otherwise the no-flag invocation `brief-validator.mjs <brief.md>` drops
+  // the file (which sits at index 0) and bails to Usage.
+  const skipIdx = minIdx >= 0 ? minIdx + 1 : -1;
+  const filePath = args.find((a, i) => !a.startsWith('--') && i !== skipIdx);
   if (!filePath) {
     process.stderr.write('Usage: brief-validator.mjs [--soft] [--min-version <x.y>] <brief.md>\n');
     process.exit(2);
diff --git a/tests/validators/brief-validator.test.mjs b/tests/validators/brief-validator.test.mjs
index a24d9d4..3a05928 100644
--- a/tests/validators/brief-validator.test.mjs
+++ b/tests/validators/brief-validator.test.mjs
@@ -1,5 +1,9 @@
 import { test } from 'node:test';
 import { strict as assert } from 'node:assert';
+import { execFileSync } from 'node:child_process';
+import { mkdtempSync, rmSync, writeFileSync } from 'node:fs';
+import { tmpdir } from 'node:os';
+import { join } from 'node:path';
 import { validateBriefContent } from '../../lib/validators/brief-validator.mjs';
 
 const GOOD_BRIEF = `---
@@ -393,3 +397,38 @@ test('validateBrief — S18 min-version: trekreview brief is exempt (no framing
   const r = validateBriefContent(REVIEW_AS_BRIEF, { minBriefVersion: '2.2' });
   assert.ok(!r.warnings.find(w => w.code === 'BRIEF_VERSION_BELOW_MINIMUM'));
 });
+
+// S56 — CLI arg-parsing regression. The no-flag invocation `brief-validator.mjs <brief.md>`
+// used to bail to Usage/exit 2 because the --min-version skip index was 0 when the flag
+// was absent, dropping the file positional (which sits at argv index 0).
+test('CLI — no-flag invocation reaches validation, does not bail to Usage (S56 regression)', () => {
+  const dir = mkdtempSync(join(tmpdir(), 'brief-cli-'));
+  try {
+    const file = join(dir, 'brief.md');
+    writeFileSync(file, GOOD_BRIEF);
+    // execFileSync throws on non-zero exit; pre-fix this bailed to Usage (exit 2).
+    const out = execFileSync(process.execPath, [
+      'lib/validators/brief-validator.mjs',
+      file,
+    ], { encoding: 'utf-8' });
+    assert.match(out, /PASS/);
+  } finally {
+    rmSync(dir, { recursive: true, force: true });
+  }
+});
+
+test('CLI — --min-version still locates the file positional after the value token (S56)', () => {
+  const dir = mkdtempSync(join(tmpdir(), 'brief-cli-'));
+  try {
+    const file = join(dir, 'brief.md');
+    writeFileSync(file, GOOD_BRIEF);
+    const out = execFileSync(process.execPath, [
+      'lib/validators/brief-validator.mjs',
+      '--min-version', '2.0',
+      file,
+    ], { encoding: 'utf-8' });
+    assert.match(out, /PASS/);
+  } finally {
+    rmSync(dir, { recursive: true, force: true });
+  }
+});