diff --git a/openssl_wrapper.cpp b/openssl_wrapper.cpp
index 2b063f5..051b45e 100644
--- a/openssl_wrapper.cpp
+++ b/openssl_wrapper.cpp
@@ -1,3 +1,4 @@
+#include <cstring>
 #include <stdexcept>
 
 #include <openssl/hmac.h>
@@ -18,7 +19,7 @@ std::vector<char> secure_random_bytes(int num) {
 }
 
 std::array<char, 32> hmac_sha3_256(const std::vector<char>& key, const std::vector<char>& data) {
-    char hmac[32];
+    char hmac[EVP_MAX_MD_SIZE];
     unsigned int md_len;
 
     if (HMAC(EVP_sha3_256(), key.data(), static_cast<int>(key.size()), reinterpret_cast<const unsigned char*>(data.data()), data.size(), reinterpret_cast<unsigned char*>(hmac), &md_len)) {
@@ -26,7 +27,9 @@ std::array<char, 32> hmac_sha3_256(const std::vector<char>& key, const std::vect
             throw std::runtime_error("hmac_sha3_256(): HMAC() returned an unexpected size");
         }
 
-        return std::to_array(hmac);
+        std::array<char, 32> ret;
+        memcpy(ret.data(), hmac, 32);
+        return ret;
     } else {
         throw OpenSSLException(ERR_get_error());
     }