diff --git a/platform/mbed_retarget.cpp b/platform/mbed_retarget.cpp
index a3bb015334..12fcb317a7 100644
--- a/platform/mbed_retarget.cpp
+++ b/platform/mbed_retarget.cpp
@@ -977,6 +977,10 @@ extern "C" void __env_unlock( struct _reent *_r )
     __rtos_env_unlock(_r);
 }
 
+#endif
+
+#if defined (__GNUC__) || defined(__CC_ARM) || (defined (__ARMCC_VERSION) && (__ARMCC_VERSION >= 6010050))
+
 #define CXA_GUARD_INIT_DONE             (1 << 0)
 #define CXA_GUARD_INIT_IN_PROGRESS      (1 << 1)
 #define CXA_GUARD_MASK                  (CXA_GUARD_INIT_DONE | CXA_GUARD_INIT_IN_PROGRESS)