diff --git a/Release/include/cpprest/details/cpprest_compat.h b/Release/include/cpprest/details/cpprest_compat.h
index 57f277aaf0..c671ce2fe5 100644
--- a/Release/include/cpprest/details/cpprest_compat.h
+++ b/Release/include/cpprest/details/cpprest_compat.h
@@ -48,8 +48,8 @@
 // No SAL on non Windows platforms
 #include "cpprest/details/nosal.h"
 
-#if not defined __cdecl
-#if defined cdecl
+#if !defined(__cdecl)
+#if defined(cdecl)
 #define __cdecl __attribute__((cdecl))
 #else // ^^^ defined cdecl ^^^ // vvv !defined cdecl vvv
 #define __cdecl