diff --git a/crypto/internal.h b/crypto/internal.h
index a77102d..a45f97b 100644
--- a/crypto/internal.h
+++ b/crypto/internal.h
@@ -1174,6 +1174,11 @@
 
 // Arithmetic functions.
 
+// The most efficient versions of these functions on GCC and Clang depend on C11
+// |_Generic|. If we ever need to call these from C++, we'll need to add a
+// variant that uses C++ overloads instead.
+#if !defined(__cplusplus)
+
 // CRYPTO_addc_* returns |x + y + carry|, and sets |*out_carry| to the carry
 // bit. |carry| must be zero or one.
 #if OPENSSL_HAS_BUILTIN(__builtin_addc)
@@ -1275,6 +1280,8 @@
 #define CRYPTO_subc_w CRYPTO_subc_u32
 #endif
 
+#endif  // !__cplusplus
+
 
 // FIPS functions.