diff --git a/native-tls-hook.js b/native-tls-hook.js
index 5cf3b5b..f450dbe 100644
--- a/native-tls-hook.js
+++ b/native-tls-hook.js
@@ -99,7 +99,7 @@ function patchTargetLib(targetLib) {
 
     const buildVerificationCallback = (realCallbackAddr) => {
         if (!verificationCallbackCache[realCallbackAddr]) {
-            const realCallback = realCallbackAddr
+            const realCallback = (!realCallbackAddr || realCallbackAddr.isNull())
                 ? new NativeFunction(realCallbackAddr, 'int', ['pointer','pointer'])
                 : () => SSL_VERIFY_INVALID; // Callback can be null - treat as invalid (=our validation only)