diff --git a/HISTORY.rst b/HISTORY.rst
index e1423599..a36f0409 100644
--- a/HISTORY.rst
+++ b/HISTORY.rst
@@ -1,10 +1,16 @@
 Release Notes
 =============
 
-.. _release_notes_4_0:
+.. _release_notes_4:
+
+PlatformIO Core 4
+-----------------
+
+4.2.1 (2020-02-??)
+~~~~~~~~~~~~~~~~~~
+
+* Fixed "TypeError: unsupported operand type(s)" when system environment variable is used by project configuration parser (`issue #3377 <https://github.com/platformio/platformio-core/issues/3377>`_)
 
-PlatformIO Core 4.0
--------------------
 
 4.2.0 (2020-02-12)
 ~~~~~~~~~~~~~~~~~~
@@ -182,8 +188,8 @@ PlatformIO Core 4.0
   - Fixed "systemd-udevd" warnings in `99-platformio-udev.rules <http://docs.platformio.org/page/faq.html#platformio-udev-rules>`__ (`issue #2442 <https://github.com/platformio/platformio-core/issues/2442>`_)
   - Fixed an issue when package cache (Library Manager) expires too fast (`issue #2559 <https://github.com/platformio/platformio-core/issues/2559>`_)
 
-PlatformIO Core 3.0
--------------------
+PlatformIO Core 3
+-----------------
 
 3.6.7 (2019-04-23)
 ~~~~~~~~~~~~~~~~~~
@@ -783,8 +789,8 @@ PlatformIO Core 3.0
   (`issue #742 <https://github.com/platformio/platformio-core/issues/742>`_)
 * Stopped supporting Python 2.6
 
-PlatformIO Core 2.0
---------------------
+PlatformIO Core 2
+-----------------
 
 2.11.2 (2016-08-02)
 ~~~~~~~~~~~~~~~~~~~
@@ -1569,8 +1575,8 @@ PlatformIO Core 2.0
 * Fixed bug with creating copies of source files
   (`issue #177 <https://github.com/platformio/platformio-core/issues/177>`_)
 
-PlatformIO Core 1.0
--------------------
+PlatformIO Core 1
+-----------------
 
 1.5.0 (2015-05-15)
 ~~~~~~~~~~~~~~~~~~
@@ -1760,8 +1766,8 @@ PlatformIO Core 1.0
   error (`issue #81 <https://github.com/platformio/platformio-core/issues/81>`_)
 * Several bug fixes, increased stability and performance improvements
 
-PlatformIO Core 0.0
--------------------
+PlatformIO Core Preview
+-----------------------
 
 0.10.2 (2015-01-06)
 ~~~~~~~~~~~~~~~~~~~
diff --git a/platformio/project/config.py b/platformio/project/config.py
index 2e063fac..4dc3c38c 100644
--- a/platformio/project/config.py
+++ b/platformio/project/config.py
@@ -273,7 +273,9 @@ class ProjectConfigBase(object):
                     if envvar_value:
                         break
             if envvar_value and option_meta.multiple:
-                value += ("" if value == MISSING else "\n") + envvar_value
+                if value == MISSING:
+                    value = ""
+                value += ("\n" if value else "") + envvar_value
             elif envvar_value and value == MISSING:
                 value = envvar_value
 
diff --git a/tests/test_projectconf.py b/tests/test_projectconf.py
index 44731875..8172e692 100644
--- a/tests/test_projectconf.py
+++ b/tests/test_projectconf.py
@@ -185,6 +185,7 @@ def test_sysenv_options(config):
     assert config.get("env:base", "upload_port") is None
     assert config.get("env:extra_2", "upload_port") == "/dev/extra_2/port"
     os.environ["PLATFORMIO_BUILD_FLAGS"] = "-DSYSENVDEPS1 -DSYSENVDEPS2"
+    os.environ["PLATFORMIO_BUILD_UNFLAGS"] = "-DREMOVE_MACRO"
     os.environ["PLATFORMIO_UPLOAD_PORT"] = "/dev/sysenv/port"
     os.environ["__PIO_TEST_CNF_EXTRA_FLAGS"] = "-L /usr/local/lib"
     assert config.get("custom", "extra_flags") == "-L /usr/local/lib"
@@ -194,6 +195,7 @@ def test_sysenv_options(config):
     ]
     assert config.get("env:base", "upload_port") == "/dev/sysenv/port"
     assert config.get("env:extra_2", "upload_port") == "/dev/extra_2/port"
+    assert config.get("env:base", "build_unflags") == ["-DREMOVE_MACRO"]
 
     # env var as option
     assert config.options(env="test_extends") == [
@@ -206,6 +208,7 @@ def test_sysenv_options(config):
         "lib_deps",
         "lib_ignore",
         "custom_builtin_option",
+        "build_unflags",
         "upload_port",
     ]
 
@@ -215,6 +218,7 @@ def test_sysenv_options(config):
 
     # cleanup system environment variables
     del os.environ["PLATFORMIO_BUILD_FLAGS"]
+    del os.environ["PLATFORMIO_BUILD_UNFLAGS"]
     del os.environ["PLATFORMIO_UPLOAD_PORT"]
     del os.environ["__PIO_TEST_CNF_EXTRA_FLAGS"]
     del os.environ["PLATFORMIO_HOME_DIR"]