diff --git a/HISTORY.rst b/HISTORY.rst
index 644d7066..63c5ab84 100644
--- a/HISTORY.rst
+++ b/HISTORY.rst
@@ -21,6 +21,8 @@ PlatformIO 3.0
   systems (Windows)
 * Fixed issue with ``build_unflags`` option when a macro contains value
   (e.g., ``-DNAME=VALUE``)
+* Fixed issue which did not allow to override runtime build environment using
+  extra POST script
 
 3.5.2 (2018-03-13)
 ~~~~~~~~~~~~~~~~~~
diff --git a/platformio/builder/main.py b/platformio/builder/main.py
index 04a19eba..8da01270 100644
--- a/platformio/builder/main.py
+++ b/platformio/builder/main.py
@@ -156,7 +156,7 @@ env.LoadPioPlatform(commonvars)
 env.SConscriptChdir(0)
 env.SConsignFile(join("$PROJECTBUILD_DIR", ".sconsign.dblite"))
 
-for item in env.GetPreExtraScripts():
+for item in env.GetExtraScripts("pre"):
     env.SConscript(item, exports="env")
 
 env.SConscript("$BUILD_SCRIPT")
@@ -167,7 +167,7 @@ AlwaysBuild(env.Alias("__test", DEFAULT_TARGETS + ["size"]))
 if "UPLOAD_FLAGS" in env:
     env.Append(UPLOADERFLAGS=["$UPLOAD_FLAGS"])
 
-for item in env.GetPostExtraScripts():
+for item in env.GetExtraScripts("post"):
     env.SConscript(item, exports="env")
 
 if "envdump" in COMMAND_LINE_TARGETS:
diff --git a/platformio/builder/tools/piomisc.py b/platformio/builder/tools/piomisc.py
index 7c08237f..69e859f3 100644
--- a/platformio/builder/tools/piomisc.py
+++ b/platformio/builder/tools/piomisc.py
@@ -18,7 +18,7 @@ import atexit
 import re
 import sys
 from os import environ, remove, walk
-from os.path import basename, isdir, isfile, join, relpath, sep
+from os.path import basename, isdir, isfile, join, realpath, relpath, sep
 from tempfile import mkstemp
 
 from SCons.Action import Action
@@ -302,18 +302,17 @@ def ProcessTest(env):
         duplicate=False)
 
 
-def GetPreExtraScripts(env):
-    return [
-        item[4:] for item in env.get("EXTRA_SCRIPTS", [])
-        if item.startswith("pre:")
-    ]
-
-
-def GetPostExtraScripts(env):
-    return [
-        item[5:] if item.startswith("post:") else item
-        for item in env.get("EXTRA_SCRIPTS", []) if not item.startswith("pre:")
-    ]
+def GetExtraScripts(env, scope):
+    items = []
+    for item in env.get("EXTRA_SCRIPTS", []):
+        if scope == "post" and ":" not in item:
+            items.append(item)
+        elif item.startswith("%s:" % scope):
+            items.append(item[len(scope) + 1:])
+    if not items:
+        return items
+    with util.cd(env.subst("$PROJECT_DIR")):
+        return [realpath(item) for item in items]
 
 
 def exists(_):
@@ -328,6 +327,5 @@ def generate(env):
     env.AddMethod(PioClean)
     env.AddMethod(ProcessDebug)
     env.AddMethod(ProcessTest)
-    env.AddMethod(GetPreExtraScripts)
-    env.AddMethod(GetPostExtraScripts)
+    env.AddMethod(GetExtraScripts)
     return env
diff --git a/platformio/builder/tools/platformio.py b/platformio/builder/tools/platformio.py
index 00649dd9..80a6cbb9 100644
--- a/platformio/builder/tools/platformio.py
+++ b/platformio/builder/tools/platformio.py
@@ -289,15 +289,14 @@ def BuildFrameworks(env, frameworks):
 
 
 def BuildLibrary(env, variant_dir, src_dir, src_filter=None):
-    lib = env.Clone()
-    return lib.StaticLibrary(
-        lib.subst(variant_dir),
-        lib.CollectBuildFiles(variant_dir, src_dir, src_filter))
+    return env.StaticLibrary(
+        env.subst(variant_dir),
+        env.CollectBuildFiles(variant_dir, src_dir, src_filter))
 
 
 def BuildSources(env, variant_dir, src_dir, src_filter=None):
-    DefaultEnvironment().Append(PIOBUILDFILES=env.Clone().CollectBuildFiles(
-        variant_dir, src_dir, src_filter))
+    DefaultEnvironment().Append(
+        PIOBUILDFILES=env.CollectBuildFiles(variant_dir, src_dir, src_filter))
 
 
 def exists(_):
diff --git a/tests/test_builder.py b/tests/test_builder.py
index a307faa9..6dd90eb7 100644
--- a/tests/test_builder.py
+++ b/tests/test_builder.py
@@ -24,9 +24,15 @@ def test_build_flags(clirunner, validate_cliresult, tmpdir):
     tmpdir.join("platformio.ini").write("""
 [env:native]
 platform = native
+extra_scripts = extra.py
 build_flags = %s
     """ % " ".join([f[0] for f in build_flags]))
 
+    tmpdir.join("extra.py").write("""
+Import("env")
+env.Append(CPPDEFINES="POST_SCRIPT_MACRO")
+    """)
+
     tmpdir.mkdir("src").join("main.cpp").write("""
 #if !defined(TEST_INT) || TEST_INT != 13
 #error "TEST_INT"
@@ -36,6 +42,10 @@ build_flags = %s
 #error "TEST_STR_SPACE"
 #endif
 
+#ifndef POST_SCRIPT_MACRO
+#error "POST_SCRIPT_MACRO"
+#endif
+
 int main() {
 }
 """)