diff --git a/src/c0vm.js b/src/c0vm.js
index 237cf44..bf8170e 100755
--- a/src/c0vm.js
+++ b/src/c0vm.js
@@ -78,6 +78,8 @@ ProgramState.prototype.push = function(val) {
 }
 
 ProgramState.prototype.pop = function() {
+    if (this.frame.stack === [])
+        throw "Tried to pop from an empty stack!";
     return this.frame.stack.pop();
 }
 
@@ -372,7 +374,7 @@ ProgramState.prototype.step = function() {
         // Read offset into a struct
         var offset = this.frame.program[this.frame.pc + 1];
         var index = this.pop();
-        this.push(this.heap[index + offset]);
+        this.push(index + offset);
         this.frame.pc += 2;
         break;
 
@@ -407,6 +409,7 @@ ProgramState.prototype.step = function() {
         for (var i = 0; i < 4; i++)
             this.heap[addr + i] = array[i];
         this.frame.pc++;
+        break;
 
     case op.AMLOAD:
         var addr = this.pop();
@@ -460,6 +463,16 @@ function execute(file, callbacks, v) {
         var val = state.step();
         if (val !== undefined) return val;
 
+        if (verbose) {
+            console.log("Machine state:");
+            console.log("  Current Stack Frame:");
+            console.log("    Stack: " + state.frame.stack);
+            console.log("    PC:    " + state.frame.pc);
+            console.log("    Vars:  " + state.frame.variables);
+            console.log("    Code:  " + state.frame.program);
+            console.log("  Heap: " + state.heap);
+        }
+
         // if (at_breakpoint) {
         //   save state (maybe in a global in this file?)
         //   return;
diff --git a/src/index.js b/src/index.js
index 09a1678..901e9a8 100644
--- a/src/index.js
+++ b/src/index.js
@@ -13,9 +13,11 @@ c0ffi = require("./c0ffi.js");
 callbacks = {};
 callbacks[c0ffi.NATIVE_PRINT] = function(args) {
     console.log("Print function says: " + args[0]);
+    return 0;
 }
 callbacks[c0ffi.NATIVE_PRINTINT] = function(args) {
     console.log("Printint function says: " + args[0]);
+    return 0;
 }
 
 console.log(callbacks);