diff --git a/lib/exceptions.js b/lib/exceptions.js
index d4bd91fd76..3f478d5ff1 100644
--- a/lib/exceptions.js
+++ b/lib/exceptions.js
@@ -5,7 +5,8 @@ const ERROR = {
   INVALID_JUMP: 'invalid JUMP',
   INVALID_OPCODE: 'invalid opcode',
   REVERT: 'revert',
-  STATIC_STATE_CHANGE: 'static state change'
+  STATIC_STATE_CHANGE: 'static state change',
+  INTERNAL_ERROR: 'internal error'
 }
 
 function VmError (error) {
diff --git a/lib/runCode.js b/lib/runCode.js
index d3e1d2d999..7d64efe4e8 100644
--- a/lib/runCode.js
+++ b/lib/runCode.js
@@ -165,11 +165,14 @@ module.exports = function (opts, cb) {
         cb(new VmError(ERROR.OUT_OF_GAS))
         return
       }
+
       // advance program counter
       runState.programCounter++
       var argsNum = opInfo.in
+      var retNum = opInfo.out
       // pop the stack
-      var args = argsNum ? runState.stack.splice(-opInfo.in) : []
+      var args = argsNum ? runState.stack.splice(-argsNum) : []
+
       args.reverse()
       args.push(runState)
       // create a callback for async opFunc
@@ -178,11 +181,20 @@ module.exports = function (opts, cb) {
           if (err) return cb(err)
 
           // save result to the stack
-          if (result) {
+          if (result !== undefined) {
+            if (retNum !== 1) {
+              // opcode post-stack mismatch
+              return cb(new VmError(ERROR.INTERNAL_ERROR))
+            }
             // NOTE: Ensure that every stack item is padded to 256 bits.
             //       This should be done at every opcode in the future.
             result = utils.setLengthLeft(result, 32)
             runState.stack.push(result)
+          } else {
+            if (retNum !== 0) {
+              // opcode post-stack mismatch
+              return cb(new VmError(ERROR.INTERNAL_ERROR))
+            }
           }
 
           cb()
@@ -198,11 +210,20 @@ module.exports = function (opts, cb) {
       }
 
       // save result to the stack
-      if (result) {
+      if (result !== undefined) {
+        if (retNum !== 1) {
+          // opcode post-stack mismatch
+          return cb(VmError(ERROR.INTERNAL_ERROR))
+        }
         // NOTE: Ensure that every stack item is padded to 256 bits.
         //       This should be done at every opcode in the future.
         result = utils.setLengthLeft(result, 32)
         runState.stack.push(result)
+      } else {
+        if (!opInfo.async && retNum !== 0) {
+          // opcode post-stack mismatch
+          return cb(VmError(ERROR.INTERNAL_ERROR))
+        }
       }
 
       // call the callback if opFn was sync