diff --git a/pkg/vm/vm_ops_maths.go b/pkg/vm/vm_ops_maths.go
index 7d6afad41..6085dccb8 100644
--- a/pkg/vm/vm_ops_maths.go
+++ b/pkg/vm/vm_ops_maths.go
@@ -7,35 +7,39 @@ import (
 // Add adds two stack Items together.
 // Returns an error if either items cannot be casted to an integer
 // or if integers cannot be added together
-func Add(op stack.Instruction, ctx *stack.Context, istack *stack.Invocation) error {
+func Add(op stack.Instruction, ctx *stack.Context, istack *stack.Invocation) (Vmstate, error) {
 
 	operandA, operandB, err := popTwoIntegers(ctx)
-
+	if err != nil {
+		return FAULT, err
+	}
 	res, err := operandA.Add(operandB)
 	if err != nil {
-		return err
+		return FAULT, err
 	}
 
 	ctx.Estack.Push(res)
 
-	return nil
+	return NONE, nil
 }
 
 // Sub subtracts two stack Items.
 // Returns an error if either items cannot be casted to an integer
 // or if integers cannot be subtracted together
-func Sub(op stack.Instruction, ctx *stack.Context, istack *stack.Invocation) error {
+func Sub(op stack.Instruction, ctx *stack.Context, istack *stack.Invocation) (Vmstate, error) {
 
 	operandA, operandB, err := popTwoIntegers(ctx)
-
+	if err != nil {
+		return FAULT, err
+	}
 	res, err := operandB.Sub(operandA)
 	if err != nil {
-		return err
+		return HALT, err
 	}
 
 	ctx.Estack.Push(res)
 
-	return nil
+	return NONE, nil
 }
 
 func popTwoIntegers(ctx *stack.Context) (*stack.Int, *stack.Int, error) {
@@ -50,3 +54,17 @@ func popTwoIntegers(ctx *stack.Context) (*stack.Int, *stack.Int, error) {
 
 	return operandA, operandB, nil
 }
+
+func popTwoByteArrays(ctx *stack.Context) (*stack.ByteArray, *stack.ByteArray, error) {
+	// Pop first stack item and cast as byte array
+	ba1, err := ctx.Estack.PopByteArray()
+	if err != nil {
+		return nil, nil, err
+	}
+	// Pop second stack item and cast as byte array
+	ba2, err := ctx.Estack.PopByteArray()
+	if err != nil {
+		return nil, nil, err
+	}
+	return ba1, ba2, nil
+}