diff --git a/platformio/builder/tools/piolib.py b/platformio/builder/tools/piolib.py
index 9831c349..fdf351bb 100644
--- a/platformio/builder/tools/piolib.py
+++ b/platformio/builder/tools/piolib.py
@@ -619,7 +619,7 @@ class ProjectAsLibBuilder(LibBuilderBase):
         return inc_dirs
 
     def get_src_files(self):
-        return self.env['PIOBUILDFILES']
+        return self.env.get("PROJECTBUILDFILES", [])
 
     @property
     def lib_ldf_mode(self):
diff --git a/platformio/builder/tools/platformio.py b/platformio/builder/tools/platformio.py
index 62f7d369..adfd6209 100644
--- a/platformio/builder/tools/platformio.py
+++ b/platformio/builder/tools/platformio.py
@@ -63,7 +63,7 @@ def BuildProgram(env):
     # Search for project source files
     env.Append(
         LIBPATH=["$BUILD_DIR"],
-        PIOBUILDFILES=env.CollectBuildFiles(
+        PROJECTBUILDFILES=env.CollectBuildFiles(
             "$BUILDSRC_DIR",
             "$PROJECTSRC_DIR",
             src_filter=env.get("SRC_FILTER"),
@@ -72,7 +72,7 @@ def BuildProgram(env):
     if "__debug" in COMMAND_LINE_TARGETS:
         env.ProcessDebug()
     if "__test" in COMMAND_LINE_TARGETS:
-        env.Append(PIOBUILDFILES=env.ProcessTest())
+        env.Append(PROJECTBUILDFILES=env.ProcessTest())
 
     # build dependent libs
     env.Append(LIBS=env.BuildProjectLibraries())
@@ -90,14 +90,15 @@ def BuildProgram(env):
     # Handle SRC_BUILD_FLAGS
     env.ProcessFlags(env.get("SRC_BUILD_FLAGS"))
 
-    if not env['PIOBUILDFILES'] and not COMMAND_LINE_TARGETS:
+    if not env.get("PROJECTBUILDFILES") and not COMMAND_LINE_TARGETS:
         sys.stderr.write(
             "Error: Nothing to build. Please put your source code files "
             "to '%s' folder\n" % env.subst("$PROJECTSRC_DIR"))
         env.Exit(1)
 
     program = env.Program(
-        join("$BUILD_DIR", env.subst("$PROGNAME")), env['PIOBUILDFILES'])
+        join("$BUILD_DIR", env.subst("$PROGNAME")),
+        env['PROJECTBUILDFILES'] + env.get("PIOBUILDFILES", []))
 
     checksize_action = Action(env.CheckUploadSize, "Checking program size")
     AlwaysBuild(env.Alias("checkprogsize", program, checksize_action))