fix

src/esm.ts

@@ -168,8 +168,14 @@ export function createEsmHooks(tsNodeService: Service) {
         if (!isProbablyEntrypoint(specifier, context.parentURL))
           throw esmResolverError;
         try {
+          let cjsSpecifier = specifier;
+          // Attempt to convert from ESM file:// to CommonJS path
+          try {
+            if (specifier.startsWith('file://'))
+              cjsSpecifier = fileURLToPath(specifier);
+          } catch {}
           const resolution = pathToFileURL(
-            createRequire(process.cwd()).resolve(specifier)
+            createRequire(process.cwd()).resolve(cjsSpecifier)
           ).toString();
           rememberIsProbablyEntrypoint.add(resolution);
           rememberResolvedViaCommonjsFallback.add(resolution);

src/test/esm-loader.spec.ts

@@ -277,7 +277,22 @@ test.suite('esm', (test) => {
 
     test.suite(
       'Entrypoint resolution falls back to CommonJS resolver and format',
-      (test) => {}
+      (test) => {
+        test('extensionless entrypoint', async (t) => {
+          const { err, stdout } = await exec(
+            `${CMD_ESM_LOADER_WITHOUT_PROJECT} ./esm-loader-entrypoint-cjs-fallback/extensionless-entrypoint`
+          );
+          expect(err).toBe(null);
+          expect(stdout.trim()).toBe('Hello world!');
+        });
+        test('relies upon CommonJS resolution', async (t) => {
+          const { err, stdout } = await exec(
+            `${CMD_ESM_LOADER_WITHOUT_PROJECT} ./esm-loader-entrypoint-cjs-fallback/relies-upon-cjs-resolution`
+          );
+          expect(err).toBe(null);
+          expect(stdout.trim()).toBe('Hello world!');
+        });
+      }
     );
   });