diff --git a/SConscript b/SConscript
index cd72820..9277fe6 100644
--- a/SConscript
+++ b/SConscript
@@ -39,8 +39,10 @@ mcu_startup_files = {
 }
 
 # Check each defined MCU, match the platform and append the appropriate startup file
+cpp_defines_tuple = env.get('CPPDEFINES', [])
+cpp_defines_list = [item[0] if isinstance(item, tuple) else item for item in cpp_defines_tuple]
 for mcu, startup_file in mcu_startup_files.items():
-    if mcu in env.get('CPPDEFINES', []):
+    if mcu in cpp_defines_list:
         if rtconfig.PLATFORM in ['gcc', 'llvm-arm']:
             src += [os.path.join(cwd, 'Source', 'Templates', 'gcc', startup_file)]
         elif rtconfig.PLATFORM in ['armcc', 'armclang']:
@@ -53,4 +55,4 @@ for mcu, startup_file in mcu_startup_files.items():
 group = DefineGroup('STM32F4-CMSIS', src, depend=['PKG_USING_STM32F4_CMSIS_DRIVER'], CPPPATH=path)
 
 # Return the build group
-Return('group')
\ No newline at end of file
+Return('group')