diff --git a/packages/api/src/routes/workspace.ts b/packages/api/src/routes/workspace.ts
index 58835cf48..b99934bda 100644
--- a/packages/api/src/routes/workspace.ts
+++ b/packages/api/src/routes/workspace.ts
@@ -280,7 +280,7 @@ export const workspaceRoutes: FastifyPluginAsync<WorkspaceRouteOpts> = async (ap
   app.get<{ Querystring: { repoRoot?: string } }>('/api/workspace/worktrees', async (request, reply) => {
     const { repoRoot } = request.query;
     if (repoRoot) {
-      if (!repoRoot.startsWith('/')) {
+      if (!isAbsolute(repoRoot)) {
         reply.status(400);
         return { error: 'repoRoot must be an absolute path' };
       }
diff --git a/packages/api/test/workspace-windows-path.test.js b/packages/api/test/workspace-windows-path.test.js
new file mode 100644
index 000000000..add41e52e
--- /dev/null
+++ b/packages/api/test/workspace-windows-path.test.js
@@ -0,0 +1,36 @@
+import assert from 'node:assert/strict';
+import { isAbsolute } from 'node:path';
+import { describe, it } from 'node:test';
+
+describe('workspace worktrees repoRoot validation (Windows compat)', () => {
+  // The route handler uses isAbsolute() to validate repoRoot.
+  // Previously it used startsWith('/') which rejected Windows paths.
+
+  it('accepts Unix absolute path', () => {
+    assert.ok(isAbsolute('/home/user/project'));
+  });
+
+  it('accepts Windows absolute path with backslash', () => {
+    assert.ok(isAbsolute('C:\\Personal\\AIProjects\\test-project'));
+  });
+
+  it('accepts Windows absolute path with forward slash', () => {
+    assert.ok(isAbsolute('C:/Personal/AIProjects/test-project'));
+  });
+
+  it('accepts UNC path', () => {
+    assert.ok(isAbsolute('\\\\server\\share\\folder'));
+  });
+
+  it('rejects relative path', () => {
+    assert.ok(!isAbsolute('relative/path'));
+  });
+
+  it('rejects dot-relative path', () => {
+    assert.ok(!isAbsolute('./src/index.ts'));
+  });
+
+  it('rejects parent-relative path', () => {
+    assert.ok(!isAbsolute('../etc/passwd'));
+  });
+});