diff --git a/tools/resources/__init__.py b/tools/resources/__init__.py
index d1b948999d..243b6c0c5d 100644
--- a/tools/resources/__init__.py
+++ b/tools/resources/__init__.py
@@ -38,7 +38,7 @@ from collections import namedtuple, defaultdict
 from copy import copy
 from itertools import chain
 from os import walk, sep
-from os.path import (join, splitext, dirname, relpath, basename, split, normcase,
+from os.path import (join, splitext, dirname, relpath, basename, split, normpath,
                      abspath, exists)
 
 from .ignore import MbedIgnoreSet, IGNORE_FILENAME
@@ -148,6 +148,11 @@ class Resources(object):
 
         self._ignoreset = MbedIgnoreSet()
 
+        # make sure mbed-os root is added as include directory
+        script_dir = dirname(abspath(__file__))
+        mbed_os_root_dir = normpath(join(script_dir, '..', '..'))
+        self.add_file_ref(FileType.INC_DIR, mbed_os_root_dir, mbed_os_root_dir)
+
     def ignore_dir(self, directory):
         if self._collect_ignores:
             self.ignored_dirs.append(directory)