diff --git a/lib/opFns.js b/lib/opFns.js
index c85340d6369..25d5acb029b 100644
--- a/lib/opFns.js
+++ b/lib/opFns.js
@@ -7,6 +7,17 @@ const constants = require('./constants.js')
 const logTable = require('./logTable.js')
 const ERROR = constants.ERROR
 
+// Find Ceil(`this` / `num`)
+BN.prototype.divCeil = function divCeil (num) {
+  var dm = this.divmod(num);
+
+  // Fast case - exact division
+  if (dm.mod.isZero()) return dm.div;
+
+  // Round up
+  return dm.div.negative !== 0 ? dm.div.isubn(1) : dm.div.iaddn(1);
+};
+
 // the opcode functions
 module.exports = {
   STOP: function (runState) {
@@ -199,7 +210,7 @@ module.exports = {
     length = new BN(length)
     var data = memLoad(runState, offset, length)
     // copy fee
-    subGas(runState, new BN(fees.sha3WordGas.v).imul(length.divRound(new BN(32))))
+    subGas(runState, new BN(fees.sha3WordGas.v).imul(length.divCeil(new BN(32))))
     return utils.sha3(data)
   },
   // 0x30 range - closure state
@@ -257,7 +268,7 @@ module.exports = {
 
     memStore(runState, memOffset, runState.callData, dataOffset, dataLength)
     // sub the COPY fee
-    subGas(runState, new BN(fees.copyGas.v).imul(dataLength.divRound(new BN(32))))
+    subGas(runState, new BN(fees.copyGas.v).imul(dataLength.divCeil(new BN(32))))
   },
   CODESIZE: function (runState) {
     return utils.intToBuffer(runState.code.length)
@@ -269,7 +280,7 @@ module.exports = {
 
     memStore(runState, memOffset, runState.code, codeOffset, length)
     // sub the COPY fee
-    subGas(runState, new BN(fees.copyGas.v).imul(length.divRound(new BN(32))))
+    subGas(runState, new BN(fees.copyGas.v).imul(length.divCeil(new BN(32))))
   },
   EXTCODESIZE: function (address, runState, cb) {
     var stateManager = runState.stateManager
@@ -289,7 +300,7 @@ module.exports = {
     // FIXME: for some reason this must come before subGas
     subMemUsage(runState, memOffset, length)
     // copy fee
-    subGas(runState, new BN(fees.copyGas.v).imul(length.divRound(new BN(32))))
+    subGas(runState, new BN(fees.copyGas.v).imul(length.divCeil(new BN(32))))
 
     stateManager.getContractCode(address, function (err, code) {
       if (err) return cb(err)
@@ -769,7 +780,7 @@ function trap (err) {
  * @return {String}
  */
 function subMemUsage (runState, offset, length) {
-  const newMemoryWordCount = offset.add(length).divRound(new BN(32))
+  const newMemoryWordCount = offset.add(length).divCeil(new BN(32))
   if (newMemoryWordCount.lte(runState.memoryWordCount)) return
   runState.memoryWordCount = newMemoryWordCount