diff --git a/build/libraries/os/common/os_printf.c b/build/libraries/os/common/os_printf.c
index 888cdcf..fea9fa6 100644
--- a/build/libraries/os/common/os_printf.c
+++ b/build/libraries/os/common/os_printf.c
@@ -286,7 +286,7 @@ static void OS_PutStringInit(const char *str)
 #if defined( SDK_DEBUGGER_ISD )
         _ISDbgLib_Initialize();
         OS_PutString = OS_PutStringISD;
-#else defined( SDK_DEBUGGER_ARM )
+#elif defined( SDK_DEBUGGER_ARM )
         OS_PutString = OS_PutStringARM;
 #endif
     }