diff --git a/include/mimalloc.h b/include/mimalloc.h
index 80cee2be..c9127e1f 100644
--- a/include/mimalloc.h
+++ b/include/mimalloc.h
@@ -24,7 +24,7 @@ terms of the MIT license. A copy of the license can be found in the file
   #define mi_attr_noexcept
 #endif
 
-#if (__cplusplus >= 201703)
+#if defined(__cplusplus) && (__cplusplus >= 201703)
   #define mi_decl_nodiscard    [[nodiscard]]
 #elif (__GNUC__ >= 4) || defined(__clang__)  // includes clang, icc, and clang-cl
   #define mi_decl_nodiscard    __attribute__((warn_unused_result))