diff --git a/lib/blockchain/chain.js b/lib/blockchain/chain.js
index a3975da5..cefcaf29 100644
--- a/lib/blockchain/chain.js
+++ b/lib/blockchain/chain.js
@@ -1928,6 +1928,7 @@ Chain.prototype.getOrphanRoot = function getOrphanRoot(hash) {
  */
 
 Chain.prototype.getProofTime = function getProofTime(to, from) {
+  var pow = this.network.pow;
   var sign, work;
 
   if (to.chainwork.cmp(from.chainwork) > 0) {
@@ -1938,8 +1939,8 @@ Chain.prototype.getProofTime = function getProofTime(to, from) {
     sign = -1;
   }
 
-  work = work.imuln(this.network.pow.targetSpacing);
-  work = work.idiv(this.tip.getProof());
+  work = work.imuln(pow.targetSpacing);
+  work = work.div(this.tip.getProof());
 
   if (work.bitLength() > 53)
     return sign * util.MAX_SAFE_INTEGER;