diff --git a/HISTORY.rst b/HISTORY.rst
index 33737527..ab73f480 100644
--- a/HISTORY.rst
+++ b/HISTORY.rst
@@ -30,10 +30,11 @@ PlatformIO Core 6
   - Do not resolve dependencies from the project "src" folder when the `test_build_src <https://docs.platformio.org/en/latest//projectconf/section_env_test.html#test-build-src>`__ option is not enabled
   - Fixed an issue when a custom `pio test --project-config <https://docs.platformio.org/en/latest/core/userguide/cmd_test.html#cmdoption-pio-test-c>`__ was not handled properly (`issue #4299 <https://github.com/platformio/platformio-core/issues/4299>`_)
 
-* Allowed to ``Import("projenv")`` in a library extra script (`issue #4305 <https://github.com/platformio/platformio-core/issues/4305>`_)
-* Improved a serial port finder for a board with predefined HWIDs
 * Documented `Stringification <https://docs.platformio.org/en/latest/projectconf/section_env_build.html#stringification>`__  – converting a macro argument into a string constant (`issue #4310 <https://github.com/platformio/platformio-core/issues/4310>`_)
 * Added ``env.StringifyMacro(value)`` helper function for the `Advanced Scripting <https://docs.platformio.org/en/latest/scripting/index.html>`__
+* Allowed to ``Import("projenv")`` in a library extra script (`issue #4305 <https://github.com/platformio/platformio-core/issues/4305>`_)
+* Improved a serial port finder for a board with predefined HWIDs
+* Fixed an issue when `build_unflags <https://docs.platformio.org/en/latest/projectconf/section_env_build.html#build-unflags>`__ operation ignores a flag value (`issue #4309 <https://github.com/platformio/platformio-core/issues/4309>`_)
 
 6.0.2 (2022-06-01)
 ~~~~~~~~~~~~~~~~~~
diff --git a/platformio/builder/tools/platformio.py b/platformio/builder/tools/platformio.py
index 3334e978..59eb6387 100644
--- a/platformio/builder/tools/platformio.py
+++ b/platformio/builder/tools/platformio.py
@@ -258,7 +258,9 @@ def ProcessUnFlags(env, flags):
             for current in env.get(key, []):
                 conditions = [
                     unflag == current,
-                    isinstance(current, (tuple, list)) and unflag[0] == current[0],
+                    not isinstance(unflag, (tuple, list))
+                    and isinstance(current, (tuple, list))
+                    and unflag == current[0],
                 ]
                 if any(conditions):
                     env[key].remove(current)