diff --git a/.changeset/978-milestone-complete-force-flag.md b/.changeset/978-milestone-complete-force-flag.md
new file mode 100644
index 000000000..be3117f51
--- /dev/null
+++ b/.changeset/978-milestone-complete-force-flag.md
@@ -0,0 +1,5 @@
+---
+type: Fixed
+pr: 982
+---
+**`gsd-tools milestone complete --force` now actually overrides the unstarted-phase guard** — the dispatcher never parsed `--force`, so the guard's own documented escape hatch was inert. (#978)
diff --git a/gsd-core/bin/gsd-tools.cjs b/gsd-core/bin/gsd-tools.cjs
index 50a2e04f1..d39deed7d 100755
--- a/gsd-core/bin/gsd-tools.cjs
+++ b/gsd-core/bin/gsd-tools.cjs
@@ -1155,7 +1155,8 @@ async function runCommand(command, args, cwd, raw, defaultValue, originalCommand
       if (subcommand === 'complete') {
         const milestoneName = parseMultiwordArg(args, 'name');
         const archivePhases = args.includes('--archive-phases');
-        milestone.cmdMilestoneComplete(cwd, args[2], { name: milestoneName, archivePhases }, raw);
+        const force = args.includes('--force');
+        milestone.cmdMilestoneComplete(cwd, args[2], { name: milestoneName, archivePhases, force }, raw);
       } else {
         error('Unknown milestone subcommand. Available: complete', ERROR_REASON.SDK_UNKNOWN_COMMAND);
       }
diff --git a/scripts/lint-regression-test-names.allowlist.json b/scripts/lint-regression-test-names.allowlist.json
index 7bb0d836d..0027a5407 100644
--- a/scripts/lint-regression-test-names.allowlist.json
+++ b/scripts/lint-regression-test-names.allowlist.json
@@ -259,5 +259,6 @@
   "bug-941-managed-hooks-registry-manifest.test.cjs",
   "bug-947-hermes-gsd-prefix.test.cjs",
   "bug-948-state-noop-write-guard.test.cjs",
-  "bug-950-quick-summary-status-complete.test.cjs"
+  "bug-950-quick-summary-status-complete.test.cjs",
+  "bug-978-milestone-complete-force.test.cjs"
 ]
diff --git a/scripts/lint-test-file-count.allowlist.json b/scripts/lint-test-file-count.allowlist.json
index 8003cfa49..ac766c5f1 100644
--- a/scripts/lint-test-file-count.allowlist.json
+++ b/scripts/lint-test-file-count.allowlist.json
@@ -47,6 +47,7 @@
     "milestone": {
       "files": [
         "bug-730-milestone-phase-details-scope.test.cjs",
+        "bug-978-milestone-complete-force.test.cjs",
         "milestone-archive.test.cjs",
         "milestone-helper.test.cjs",
         "milestone-prefixed-convention.test.cjs",
diff --git a/tests/bug-978-milestone-complete-force.test.cjs b/tests/bug-978-milestone-complete-force.test.cjs
new file mode 100644
index 000000000..8cd74c883
--- /dev/null
+++ b/tests/bug-978-milestone-complete-force.test.cjs
@@ -0,0 +1,89 @@
+'use strict';
+
+/**
+ * Regression test for bug #978: `gsd-tools milestone complete --force` was a
+ * dead flag.  The milestone source (src/milestone.cts) has a guard that checks
+ * `options.force` and tells users to "Re-run with --force to override", but the
+ * CLI dispatcher (gsd-core/bin/gsd-tools.cjs) never parsed `--force` and never
+ * passed it into the options object.  So `options.force` was always `undefined`
+ * and the guard could never be overridden regardless of what the user typed.
+ */
+
+const { test, describe, beforeEach, afterEach } = require('node:test');
+const assert = require('node:assert/strict');
+const fs = require('fs');
+const path = require('path');
+const { runGsdTools, createTempProject, cleanup } = require('./helpers.cjs');
+
+/**
+ * Build a fixture where the guard will fire:
+ *  - STATE.md has `milestone: <version>` so the guard's version-match check is
+ *    satisfied.
+ *  - ROADMAP.md lists a `### Phase 999.1: Backlog Work` heading for that
+ *    milestone, but there is NO on-disk phase directory for it.
+ *
+ * This guarantees "unstarted phase" detection without touching any real phases.
+ */
+function makeGuardFixture(tmpDir, version) {
+  // STATE.md with frontmatter milestone field matching the version
+  fs.writeFileSync(
+    path.join(tmpDir, '.planning', 'STATE.md'),
+    `---\nmilestone: ${version}\n---\n# State\n\n**Status:** In progress\n**Last Activity:** 2025-01-01\n**Last Activity Description:** Working\n`,
+  );
+
+  // ROADMAP.md — the heading must include the version so getMilestonePhaseFilter
+  // does not return missingExplicitVersion.  Phase 999.1 has no on-disk dir.
+  fs.writeFileSync(
+    path.join(tmpDir, '.planning', 'ROADMAP.md'),
+    `# Roadmap ${version}\n\n### Phase 999.1: Backlog Work\n**Goal:** Not started\n`,
+  );
+}
+
+describe('bug-978: milestone complete --force overrides unstarted-phase guard', () => {
+  let tmpDir;
+
+  beforeEach(() => {
+    tmpDir = createTempProject('gsd-bug-978-');
+  });
+
+  afterEach(() => {
+    cleanup(tmpDir);
+  });
+
+  test('without --force the guard fires and emits the documented error message', () => {
+    makeGuardFixture(tmpDir, 'v1.0');
+
+    const result = runGsdTools(
+      ['milestone', 'complete', 'v1.0', '--name', 'Regression Test'],
+      tmpDir,
+    );
+
+    assert.strictEqual(result.success, false, 'command should fail without --force');
+    assert.ok(
+      result.error.includes('Re-run with --force to override'),
+      `expected guard error message; got: ${result.error}`,
+    );
+  });
+
+  test('with --force the guard is bypassed and the command succeeds', () => {
+    makeGuardFixture(tmpDir, 'v1.0');
+
+    const result = runGsdTools(
+      ['milestone', 'complete', 'v1.0', '--name', 'Regression Test', '--force'],
+      tmpDir,
+    );
+
+    assert.ok(
+      result.success,
+      `command should succeed with --force but failed: ${result.error}`,
+    );
+
+    const output = JSON.parse(result.output);
+    assert.strictEqual(output.version, 'v1.0');
+    // Milestone entry should have been created even though phase 999.1 has no dir
+    assert.ok(
+      fs.existsSync(path.join(tmpDir, '.planning', 'MILESTONES.md')),
+      'MILESTONES.md should have been created',
+    );
+  });
+});