diff --git a/src/crypto/crypto_x509.cc b/src/crypto/crypto_x509.cc
index 11622d823bbc0a..f40f6dd4f2bcaf 100644
--- a/src/crypto/crypto_x509.cc
+++ b/src/crypto/crypto_x509.cc
@@ -253,8 +253,8 @@ MaybeLocal<Value> GetSignatureAlgorithmOID(Environment* env,
 
 MaybeLocal<Value> GetSerialNumber(Environment* env, const X509View& view) {
   if (auto serial = view.getSerialNumber()) {
-    return OneByteString(env->isolate(),
-                         static_cast<unsigned char*>(serial.get()));
+    return ToV8Value(
+        env, ToUpper(std::string_view(static_cast<char*>(serial.get()))));
   }
   return Undefined(env->isolate());
 }