diff --git a/lib/bcoin/mempool.js b/lib/bcoin/mempool.js
index b3c78ea0..b10c0683 100644
--- a/lib/bcoin/mempool.js
+++ b/lib/bcoin/mempool.js
@@ -865,7 +865,7 @@ Mempool.prototype.removeUnchecked = function removeUnchecked(entry, limit, callb
  */
 
 Mempool.prototype.getMinRate = function getMinRate() {
-  var now, halflife, exp;
+  var now, halflife, size;
 
   if (!this.blockSinceBump || this.minFeeRate === 0)
     return this.minFeeRate;
@@ -874,10 +874,11 @@ Mempool.prototype.getMinRate = function getMinRate() {
 
   if (now > this.lastFeeUpdate + 10) {
     halflife = constants.mempool.FEE_HALFLIFE;
+    size = this.getSize();
 
-    if (this.size < this.maxSize / 4)
+    if (size < this.maxSize / 4)
       halflife >>>= 2;
-    else if (this.size < this.maxSize / 2)
+    else if (size < this.maxSize / 2)
       halflife >>>= 1;
 
     this.minFeeRate /= Math.pow(2.0, (now - this.lastFeeUpdate) / halflife | 0);