diff --git a/src/icon-composer.ts b/src/icon-composer.ts
index 7e101949..96282338 100644
--- a/src/icon-composer.ts
+++ b/src/icon-composer.ts
@@ -6,7 +6,27 @@ import path from 'node:path';
 import plist from 'plist';
 import semver from 'semver';
 
-export async function generateAssetCatalogForIcon(inputPath: string) {
+// `actool` is not guaranteed to produce a byte-identical `Assets.car` across
+// invocations, so when building a universal app we must compile each `.icon`
+// exactly once and reuse the output for every architecture. Otherwise the
+// per-arch `Assets.car` files differ and the universal stitch fails. The cache
+// is keyed by the resolved input path and lives for the duration of the process,
+// which spans both arch slices of a universal build.
+const assetCatalogCache = new Map<string, Promise<Buffer>>();
+
+export function generateAssetCatalogForIcon(inputPath: string): Promise<Buffer> {
+  const cacheKey = path.resolve(inputPath);
+  let assetCatalog = assetCatalogCache.get(cacheKey);
+  if (!assetCatalog) {
+    assetCatalog = compileAssetCatalogForIcon(inputPath);
+    // Don't cache failures so a transient `actool` error can be retried.
+    assetCatalog.catch(() => assetCatalogCache.delete(cacheKey));
+    assetCatalogCache.set(cacheKey, assetCatalog);
+  }
+  return assetCatalog;
+}
+
+async function compileAssetCatalogForIcon(inputPath: string) {
   if (!semver.gte(os.release(), '25.0.0')) {
     throw new Error(`actool .icon support is currently limited to macOS 26 and higher`);
   }
diff --git a/test/icon-composer.spec.ts b/test/icon-composer.spec.ts
new file mode 100644
index 00000000..9887d940
--- /dev/null
+++ b/test/icon-composer.spec.ts
@@ -0,0 +1,71 @@
+import fs from 'node:fs/promises';
+import os from 'node:os';
+import path from 'node:path';
+
+import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest';
+
+const spawn = vi.hoisted(() => vi.fn());
+
+vi.mock('@malept/cross-spawn-promise', () => ({ spawn }));
+
+const VERSION_PLIST = `<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
+<plist version="1.0">
+<dict>
+  <key>com.apple.actool.version</key>
+  <dict>
+    <key>short-bundle-version</key>
+    <string>26.0.0</string>
+  </dict>
+</dict>
+</plist>`;
+
+describe('generateAssetCatalogForIcon', () => {
+  beforeEach(() => {
+    vi.spyOn(os, 'release').mockReturnValue('26.0.0');
+    spawn.mockImplementation(async (_cmd: string, args: string[]) => {
+      if (args[0] === '--version') {
+        return VERSION_PLIST;
+      }
+      // The `--compile` invocation: emulate `actool` writing the catalog.
+      const outputPath = args[args.indexOf('--compile') + 1];
+      await fs.writeFile(path.resolve(outputPath, 'Assets.car'), 'compiled');
+      return '';
+    });
+  });
+
+  afterEach(() => {
+    vi.restoreAllMocks();
+  });
+
+  it('compiles each unique icon only once and reuses the result', async () => {
+    // Import lazily with a fresh module so the module-level cache starts empty.
+    vi.resetModules();
+    const { generateAssetCatalogForIcon } = await import('../src/icon-composer.js');
+
+    const iconA = path.resolve(os.tmpdir(), 'A.icon');
+    const iconB = path.resolve(os.tmpdir(), 'B.icon');
+    await fs.mkdir(iconA, { recursive: true });
+    await fs.mkdir(iconB, { recursive: true });
+
+    const compileCalls = () =>
+      spawn.mock.calls.filter((call) => (call[1] as string[]).includes('--compile')).length;
+
+    const [first, second] = await Promise.all([
+      generateAssetCatalogForIcon(iconA),
+      generateAssetCatalogForIcon(iconA),
+    ]);
+    // Same input path -> `actool --compile` runs exactly once.
+    expect(compileCalls()).toBe(1);
+    expect(first.equals(second)).toBe(true);
+
+    // A relative path resolving to the same icon hits the cache too.
+    const third = await generateAssetCatalogForIcon(path.relative(process.cwd(), iconA));
+    expect(compileCalls()).toBe(1);
+    expect(third.equals(first)).toBe(true);
+
+    // A different icon compiles again.
+    await generateAssetCatalogForIcon(iconB);
+    expect(compileCalls()).toBe(2);
+  });
+});