diff --git a/lib/blockchain/chain.js b/lib/blockchain/chain.js
index 6c3c8fd1..6da67e02 100644
--- a/lib/blockchain/chain.js
+++ b/lib/blockchain/chain.js
@@ -2458,7 +2458,7 @@ class Chain extends AsyncEmitter {
     factor = factor.mul(exponent.sqr()).mul(exponent);
     factor = factor.add(new BN(140737488355328));
 
-    factor.ushrn(48);
+    factor = factor.ushrn(48);
 
     target.mul(factor).add(radix);