diff --git a/HISTORY.rst b/HISTORY.rst
index 0e692fe1..eb4a3795 100644
--- a/HISTORY.rst
+++ b/HISTORY.rst
@@ -9,12 +9,14 @@ PlatformIO 3.0
 
 * Generate an `include <http://docs.platformio.org/page/projectconf/section_platformio.html#include-dir>`__
   directory with a README file when initializing a new project
+* Support in-line comments for multi-line value (``lib_deps``, ``build_flags``, etc) in `“platformio.ini” (Project Configuration File) <https://docs.platformio.org/page/projectconf.html>`__
+* Improved `PIO Unified Debugger <https://docs.platformio.org/en/page/plus/debugging.html>`__
+  for "mbed" framework and fixed issue with missed local variables
 * Introduced `"Release" and "Debug" Build Configurations <http://docs.platformio.org/page/projectconf/build_configurations.html>`__
 * Build project in "Debug Mode" including debug information with a new
   ``debug`` target using `platformio run <https://docs.platformio.org/page/userguide/cmd_run.html>`__ command or `targets <http://docs.platformio.org/page/projectconf/section_env_general.html#targets>`__ option in ``platformio.ini``.
   The last option allows to avoid project rebuilding between "Run/Debug" modes.
   (`issue #1833 <https://github.com/platformio/platformio-core/issues/1833>`_)
-* Support in-line comments for multi-line value (``lib_deps``, ``build_flags``, etc) in `“platformio.ini” (Project Configuration File) <https://docs.platformio.org/page/projectconf.html>`__
 * Do not re-create ".gitignore" and ".travis.yml" files if they were removed
   from a project
 * Report about outdated `99-platformio-udev.rules <http://docs.platformio.org/page/faq.html#platformio-udev-rules>`__
@@ -30,7 +32,6 @@ PlatformIO 3.0
   space is used in path
   (`issue #1873 <https://github.com/platformio/platformio-core/issues/1873>`_)
 
-
 3.6.0 (2018-08-06)
 ~~~~~~~~~~~~~~~~~~
 
diff --git a/platformio/builder/tools/piomisc.py b/platformio/builder/tools/piomisc.py
index ec565b51..e6628a83 100644
--- a/platformio/builder/tools/piomisc.py
+++ b/platformio/builder/tools/piomisc.py
@@ -288,10 +288,15 @@ def PioClean(env, clean_dir):
 def ProcessDebug(env):
     if not env.subst("$PIODEBUGFLAGS"):
         env.Replace(PIODEBUGFLAGS=["-Og", "-g3", "-ggdb3"])
-    env.Append(PIODEBUGFLAGS=["-D__PLATFORMIO_DEBUG__"])
     env.Append(
-        BUILD_FLAGS=env.get("PIODEBUGFLAGS", []),
-        BUILD_UNFLAGS=["-Os", "-O0", "-O1", "-O2", "-O3"])
+        PIODEBUGFLAGS=["-D__PLATFORMIO_DEBUG__"],
+        BUILD_FLAGS=env.get("PIODEBUGFLAGS", [])
+    )
+    unflags = ["-Os"]
+    for level in [0, 1, 2]:
+        for flag in ("O", "g", "ggdb"):
+            unflags.append("-%s%d" % (flag, level))
+    env.Append(BUILD_UNFLAGS=unflags)
 
 
 def ProcessTest(env):