diff --git a/include/jwt/algorithm.hpp b/include/jwt/algorithm.hpp
index 77632fb..69ce5db 100644
--- a/include/jwt/algorithm.hpp
+++ b/include/jwt/algorithm.hpp
@@ -518,7 +518,7 @@ private:
    */
   static std::string public_key_ser(EVP_PKEY* pkey, jwt::string_view sign, std::error_code& ec);
 
-#if OPENSSL_VERSION_NUMBER < 0x10100000L || LIBRESSL_VERSION_NUMBER < 0x20700000L
+#if defined(OPENSSL_VERSION_NUMBER) && OPENSSL_VERSION_NUMBER < 0x10100000L || defined(LIBRESSL_VERSION_NUMBER) && LIBRESSL_VERSION_NUMBER < 0x20700000L
 
   //ATTN: Below 2 functions
   //are Taken from https://github.com/nginnever/zogminer/issues/39