diff --git a/src/debugpy/_vendored/pydevd/pydevd_file_utils.py b/src/debugpy/_vendored/pydevd/pydevd_file_utils.py
index ab13b2bc..7ca38344 100644
--- a/src/debugpy/_vendored/pydevd/pydevd_file_utils.py
+++ b/src/debugpy/_vendored/pydevd/pydevd_file_utils.py
@@ -89,10 +89,13 @@ def _get_library_dir():
 
     if library_dir is None or not os_path_exists(library_dir):
         if hasattr(os, "__file__"):
+            # "os" is a frozen import an thus "os.__file__" is not always set.
+            # See https://github.com/python/cpython/pull/28656
             library_dir = os.path.dirname(os.__file__)
-
-    if library_dir is None:
-        library_dir = ""  # not possible to detect library_dir
+        else:
+            # "threading" is not a frozen import an thus "threading.__file__" is always set.
+            import threading
+            library_dir = os.path.dirname(threading.__file__)
 
     return library_dir