diff --git a/lib/internal/modules/package_map.js b/lib/internal/modules/package_map.js
index 0bee02a20789a1..38e7e12206c9ce 100644
--- a/lib/internal/modules/package_map.js
+++ b/lib/internal/modules/package_map.js
@@ -140,6 +140,8 @@ class PackageMap {
    * @returns {string|null}
    */
   #getKeyForPath(filePath) {
+    filePath = pathResolve(filePath);
+
     const cached = this.#pathToKeyCache.get(filePath);
     if (cached !== undefined) { return cached; }
 
diff --git a/test/parallel/test-require-package-map.js b/test/parallel/test-require-package-map.js
index b65a8f4db5a7da..87786d62738a41 100644
--- a/test/parallel/test-require-package-map.js
+++ b/test/parallel/test-require-package-map.js
@@ -300,6 +300,22 @@ describe('CJS: --experimental-package-map', { concurrency: !process.env.TEST_PAR
   describe('longest path wins', () => {
     const longestPathMap = fixtures.path('package-map/package-map-longest-path.json');
 
+    it('resolves from createRequire() paths with mixed separators', () => {
+      const { status, stdout, stderr } = spawnSync(process.execPath, [
+        '--no-warnings',
+        '--experimental-package-map', longestPathMap,
+        '-e',
+        `const { createRequire } = require('node:module'); const req = createRequire(process.cwd() + '/node_modules/inner/index.js'); const dep = req('dep-a'); console.log(dep.default);`,
+      ], {
+        cwd: fixtures.path('package-map/root'),
+        encoding: 'utf8',
+      });
+
+      assert.strictEqual(stderr, '');
+      assert.match(stdout, /dep-a-value/);
+      assert.strictEqual(status, 0, stderr);
+    });
+
     it('resolves nested package using its own dependencies, not the parent', () => {
       // Inner lives at ./root/node_modules/inner which is inside root's
       // path (./root). The longest matching path should win, so code in