diff --git a/lib/opFns.js b/lib/opFns.js
index 71c5a8d3ac..2d3ba8e217 100644
--- a/lib/opFns.js
+++ b/lib/opFns.js
@@ -470,6 +470,8 @@ module.exports = {
     return loaded
   },
   DUP: function (runState) {
+    // NOTE: this function manipulates the stack directly!
+
     const stackPos = runState.opCode - 0x7f
     if (stackPos > runState.stack.length) {
       trap(ERROR.STACK_UNDERFLOW)
@@ -478,6 +480,8 @@ module.exports = {
     return runState.stack[runState.stack.length - stackPos]
   },
   SWAP: function (runState) {
+    // NOTE: this function manipulates the stack directly!
+
     var stackPos = runState.opCode - 0x8f
 
     // check the stack to make sure we have enough items on teh stack
@@ -487,9 +491,10 @@ module.exports = {
     }
 
     // preform the swap
-    var newTop = runState.stack[swapIndex]
-    runState.stack[swapIndex] = runState.stack.pop()
-    return newTop
+    var topIndex = runState.stack.length - 1
+    var tmp = runState.stack[topIndex]
+    runState.stack[topIndex] = runState.stack[swapIndex]
+    runState.stack[swapIndex] = tmp
   },
   LOG: function (memOffset, memLength) {
     var args = Array.prototype.slice.call(arguments, 0)
@@ -1023,8 +1028,7 @@ function makeCall (runState, callOptions, localOpts, cb) {
   // check if account has enough ether
   // Note: in the case of delegatecall, the value is persisted and doesn't need to be deducted again
   if (runState.depth >= fees.stackLimit.v || (callOptions.delegatecall !== true && new BN(runState.contract.balance).lt(callOptions.value))) {
-    runState.stack.push(Buffer.from([0]))
-    cb(null)
+    cb(null, Buffer.from([0]))
   } else {
     // if creating a new contract then increament the nonce
     if (!callOptions.to) {