diff --git a/platformio/builder/main.py b/platformio/builder/main.py
index 15b0dab8..335b2ccf 100644
--- a/platformio/builder/main.py
+++ b/platformio/builder/main.py
@@ -17,6 +17,7 @@ commonvars.AddVariables(
     ("PLATFORM",),
     ("FRAMEWORK",),
     ("BUILD_FLAGS",),
+    ("SRCBUILD_FLAGS",),
 
     # board options
     ("BOARD",),
diff --git a/platformio/builder/tools/platformio.py b/platformio/builder/tools/platformio.py
index cc9ca226..3b0269cc 100644
--- a/platformio/builder/tools/platformio.py
+++ b/platformio/builder/tools/platformio.py
@@ -43,6 +43,8 @@ def BuildFirmware(env, libslist):
         if _libs:
             libslist += _libs
 
+    src.MergeFlags(getenv("PIOSRCBUILD_FLAGS", "$SRCBUILD_FLAGS"))
+
     return src.Program(
         join("$BUILD_DIR", "firmware"),
         [src.GlobCXXFiles(vdir) for vdir in vdirs],