diff --git a/lib/internal/test_runner/runner.js b/lib/internal/test_runner/runner.js
index dc6529c220539a..ee587e041a9d7f 100644
--- a/lib/internal/test_runner/runner.js
+++ b/lib/internal/test_runner/runner.js
@@ -18,6 +18,7 @@ const {
   ObjectAssign,
   PromisePrototypeThen,
   PromiseWithResolvers,
+  RegExpPrototypeSymbolReplace,
   SafeMap,
   SafePromiseAll,
   SafePromiseAllReturnVoid,
@@ -34,6 +35,7 @@ const {
 } = primordials;
 
 const { spawn } = require('child_process');
+const { statSync } = require('fs');
 const { finished } = require('internal/streams/end-of-stream');
 const { availableParallelism } = require('os');
 const { resolve, sep, isAbsolute } = require('path');
@@ -153,6 +155,23 @@ function createTestFileList(patterns, cwd) {
   const hasUserSuppliedPattern = patterns != null;
   if (!patterns || patterns.length === 0) {
     patterns = [kDefaultPattern];
+  } else {
+    patterns = ArrayPrototypeMap(patterns, (pattern) => {
+      // A directory argument is expanded to search for the default test files
+      // within it, matching the behavior from before glob patterns were
+      // supported. Glob patterns always use forward slashes, so a trailing
+      // path separator (of either kind) is stripped before appending.
+      const resolved = isAbsolute(pattern) ? pattern : resolve(cwd, pattern);
+      try {
+        if (statSync(resolved).isDirectory()) {
+          return `${RegExpPrototypeSymbolReplace(/[\\/]+$/, pattern, '')}/${kDefaultPattern}`;
+        }
+      } catch {
+        // Not a directory or not accessible; leave the pattern as-is so the
+        // existing "Could not find" handling still applies.
+      }
+      return pattern;
+    });
   }
   const glob = new Glob(patterns, {
     __proto__: null,
diff --git a/test/parallel/test-runner-cli.js b/test/parallel/test-runner-cli.js
index f563d67d1a9a41..0702c5c1500c29 100644
--- a/test/parallel/test-runner-cli.js
+++ b/test/parallel/test-runner-cli.js
@@ -62,6 +62,27 @@ for (const isolation of ['none', 'process']) {
     assert.doesNotMatch(stdout, /ok 4 - this should pass/);
   }
 
+  {
+    // A directory argument is searched for the default test files within it,
+    // both bare and with a trailing separator.
+    // Refs: https://github.com/nodejs/node/issues/64555
+    for (const dir of ['matching-patterns', 'matching-patterns/']) {
+      const args = ['--test', '--test-reporter=tap',
+                    '--no-experimental-strip-types',
+                    `--test-isolation=${isolation}`, dir];
+      const child = spawnSync(process.execPath, args, { cwd: testFixtures });
+
+      assert.strictEqual(child.status, 0);
+      assert.strictEqual(child.signal, null);
+      assert.strictEqual(child.stderr.toString(), '');
+      const stdout = child.stdout.toString();
+
+      assert.match(stdout, /ok 1 - this should pass/);
+      assert.match(stdout, /ok 2 - this should pass/);
+      assert.match(stdout, /ok 3 - this should pass/);
+    }
+  }
+
   {
     // Should match files with "-test.(c|m)(t|j)s" suffix when typescript support is enabled
     const args = ['--test', '--test-reporter=tap', '--no-warnings',