diff --git a/src/libsodium/include/sodium/utils.h b/src/libsodium/include/sodium/utils.h
index 5fec3ec6..a2af546a 100644
--- a/src/libsodium/include/sodium/utils.h
+++ b/src/libsodium/include/sodium/utils.h
@@ -10,10 +10,12 @@
 extern "C" {
 #endif
 
-#if defined(__cplusplus) || !defined(__STDC_VERSION__) || __STDC_VERSION__ < 199901L
-# define SODIUM_C99(X)
-#else
-# define SODIUM_C99(X) X
+#ifndef SODIUM_C99
+# if defined(__cplusplus) || !defined(__STDC_VERSION__) || __STDC_VERSION__ < 199901L
+#  define SODIUM_C99(X)
+# else
+#  define SODIUM_C99(X) X
+# endif
 #endif
 
 SODIUM_EXPORT