diff --git a/HISTORY.rst b/HISTORY.rst
index c9416975..65613517 100644
--- a/HISTORY.rst
+++ b/HISTORY.rst
@@ -4,6 +4,12 @@ Release Notes
 PlatformIO 3.0
 --------------
 
+3.5.2 (2018-??-??)
+~~~~~~~~~~~~~~~~~~
+
+* Handle "os.mbed.com" URL as Mercurial (hg) repository
+* Improved support for old mbed libraries without manifest
+
 3.5.1 (2018-01-18)
 ~~~~~~~~~~~~~~~~~~
 
diff --git a/platformio/builder/tools/piolib.py b/platformio/builder/tools/piolib.py
index 01cd4f2f..a6bd70e6 100644
--- a/platformio/builder/tools/piolib.py
+++ b/platformio/builder/tools/piolib.py
@@ -516,8 +516,20 @@ class MbedLibBuilder(LibBuilderBase):
         include_dirs = LibBuilderBase.get_include_dirs(self)
         if self.path not in include_dirs:
             include_dirs.append(self.path)
+
+        # library with module.json
         for p in self._manifest.get("extraIncludes", []):
             include_dirs.append(join(self.path, p))
+
+        # old mbed library without manifest, add to CPPPATH all folders
+        if not self._manifest:
+            for root, _, __ in os.walk(self.path):
+                part = root.replace(self.path, "").lower()
+                if any(s in part for s in ("%s." % sep, "test", "example")):
+                    continue
+                if root not in include_dirs:
+                    include_dirs.append(root)
+
         return include_dirs
 
     def is_frameworks_compatible(self, frameworks):