diff --git a/builtin-functions/kphp-light/stdlib/file-functions.txt b/builtin-functions/kphp-light/stdlib/file-functions.txt
index a04f361f1a..4de0dff12c 100644
--- a/builtin-functions/kphp-light/stdlib/file-functions.txt
+++ b/builtin-functions/kphp-light/stdlib/file-functions.txt
@@ -48,6 +48,8 @@ function file_exists ($name ::: string) ::: bool;
 
 function file ($name ::: string) ::: string[] | false;
 
+function is_dir ($name ::: string) ::: bool;
+
 function is_file ($name ::: string) ::: bool;
 
 function fgets ($stream ::: mixed, $length ::: int = -1) ::: string | false;
@@ -66,8 +68,6 @@ function filectime ($name ::: string) ::: int | false;
 /** @kphp-extern-func-info stub generation-required */
 function filemtime ($name ::: string) ::: int | false;
 /** @kphp-extern-func-info stub generation-required */
-function is_dir ($name ::: string) ::: bool;
-/** @kphp-extern-func-info stub generation-required */
 function is_readable ($name ::: string) ::: bool;
 /** @kphp-extern-func-info stub generation-required */
 function mkdir ($name ::: string, $mode ::: int = 0777, $recursive ::: bool = false) ::: bool;
diff --git a/runtime-light/stdlib/file/file-system-functions.h b/runtime-light/stdlib/file/file-system-functions.h
index ea10a4fa63..8741257e5f 100644
--- a/runtime-light/stdlib/file/file-system-functions.h
+++ b/runtime-light/stdlib/file/file-system-functions.h
@@ -237,6 +237,15 @@ inline Optional<array<string>> f$file(const string& name) noexcept {
   return result;
 }
 
+inline bool f$is_dir(const string& name) noexcept {
+  struct stat stat_buf {};
+  // TODO: the semantics in PHP are different: PHP expects stat
+  if (!k2::lstat(name.c_str(), std::addressof(stat_buf)).has_value()) {
+    return false;
+  }
+  return S_ISDIR(stat_buf.st_mode);
+}
+
 inline bool f$is_file(const string& name) noexcept {
   struct stat stat_buf {};
   // TODO: the semantics in PHP are different: PHP expects stat
diff --git a/tests/phpt/dl/473_file_for_k2.php b/tests/phpt/dl/473_file_for_k2.php
index 1d40c542c2..08414fe1f4 100644
--- a/tests/phpt/dl/473_file_for_k2.php
+++ b/tests/phpt/dl/473_file_for_k2.php
@@ -8,6 +8,8 @@
   var_dump (basename ('/etc/sudoers.d', '.d'));
 
   $filename = '/tmp/' . rand(1, 2e9);
+  var_dump (is_dir ('/tmp'));
+  var_dump (is_dir ($filename));
   var_dump (is_file ($filename));
 //  var_dump ($filename);
   $file = fopen ($filename, "w");