diff --git a/pkg/io/binaryBufWriter.go b/pkg/io/binaryBufWriter.go
index 31ba262ac..7015082e1 100644
--- a/pkg/io/binaryBufWriter.go
+++ b/pkg/io/binaryBufWriter.go
@@ -19,6 +19,11 @@ func NewBufBinWriter() *BufBinWriter {
 	return &BufBinWriter{BinWriter: NewBinWriterFromIO(b), buf: b}
 }
 
+// Len returns the number of bytes of the unread portion of the buffer.
+func (bw *BufBinWriter) Len() int {
+	return bw.buf.Len()
+}
+
 // Bytes returns resulting buffer and makes future writes return an error.
 func (bw *BufBinWriter) Bytes() []byte {
 	if bw.Err != nil {
diff --git a/pkg/io/binaryWriter.go b/pkg/io/binaryWriter.go
index 19086e255..d3d5503e1 100644
--- a/pkg/io/binaryWriter.go
+++ b/pkg/io/binaryWriter.go
@@ -93,6 +93,11 @@ func (w *BinWriter) WriteVarUint(val uint64) {
 
 }
 
+// WriteVarBytes writes a variable byte into the underlying io.Writer without prefix.
+func (w *BinWriter) WriteVarBytes(b []byte) {
+	w.WriteLE(b)
+}
+
 // WriteBytes writes a variable length byte array into the underlying io.Writer.
 func (w *BinWriter) WriteBytes(b []byte) {
 	w.WriteVarUint(uint64(len(b)))
diff --git a/pkg/io/binaryrw_test.go b/pkg/io/binaryrw_test.go
index 672e14ffd..4cdfbac2d 100644
--- a/pkg/io/binaryrw_test.go
+++ b/pkg/io/binaryrw_test.go
@@ -53,6 +53,13 @@ func TestWriteBE(t *testing.T) {
 	assert.Equal(t, val, readval)
 }
 
+func TestBufBinWriter_Len(t *testing.T) {
+	val := []byte{0xde}
+	bw := NewBufBinWriter()
+	bw.WriteLE(val)
+	require.Equal(t, 1, bw.Len())
+}
+
 func TestWriterErrHandling(t *testing.T) {
 	var badio = &badRW{}
 	bw := NewBinWriterFromIO(badio)
diff --git a/pkg/vm/compiler/codegen.go b/pkg/vm/compiler/codegen.go
index f54d0f844..b081784cb 100644
--- a/pkg/vm/compiler/codegen.go
+++ b/pkg/vm/compiler/codegen.go
@@ -1,7 +1,6 @@
 package compiler
 
 import (
-	"bytes"
 	"encoding/binary"
 	"go/ast"
 	"go/constant"
@@ -13,6 +12,7 @@ import (
 	"strings"
 
 	"github.com/CityOfZion/neo-go/pkg/crypto"
+	"github.com/CityOfZion/neo-go/pkg/io"
 	"github.com/CityOfZion/neo-go/pkg/vm"
 )
 
@@ -24,7 +24,7 @@ type codegen struct {
 	buildInfo *buildInfo
 
 	// prog holds the output buffer.
-	prog *bytes.Buffer
+	prog *io.BufBinWriter
 
 	// Type information.
 	typeInfo *types.Info
@@ -56,6 +56,10 @@ func (c *codegen) pc() int {
 }
 
 func (c *codegen) emitLoadConst(t types.TypeAndValue) {
+	if c.prog.Err != nil {
+		log.Fatal(c.prog.Err)
+		return
+	}
 	switch typ := t.Type.Underlying().(type) {
 	case *types.Basic:
 		switch typ.Kind() {
@@ -201,6 +205,10 @@ func (c *codegen) convertFuncDecl(file ast.Node, decl *ast.FuncDecl) {
 }
 
 func (c *codegen) Visit(node ast.Node) ast.Visitor {
+	if c.prog.Err != nil {
+		log.Fatal(c.prog.Err)
+		return nil
+	}
 	switch n := node.(type) {
 
 	// General declarations.
@@ -761,11 +769,11 @@ func (c *codegen) newFunc(decl *ast.FuncDecl) *funcScope {
 }
 
 // CodeGen compiles the program to bytecode.
-func CodeGen(info *buildInfo) (*bytes.Buffer, error) {
+func CodeGen(info *buildInfo) ([]byte, error) {
 	pkg := info.program.Package(info.initialPackage)
 	c := &codegen{
 		buildInfo: info,
-		prog:      new(bytes.Buffer),
+		prog:      io.NewBufBinWriter(),
 		l:         []int{},
 		funcs:     map[string]*funcScope{},
 		typeInfo:  &pkg.Info,
@@ -815,9 +823,12 @@ func CodeGen(info *buildInfo) (*bytes.Buffer, error) {
 		}
 	}
 
-	c.writeJumps()
-
-	return c.prog, nil
+	if c.prog.Err != nil {
+		return nil, c.prog.Err
+	}
+	buf := c.prog.Bytes()
+	c.writeJumps(buf)
+	return buf, nil
 }
 
 func (c *codegen) resolveFuncDecls(f *ast.File) {
@@ -831,8 +842,7 @@ func (c *codegen) resolveFuncDecls(f *ast.File) {
 	}
 }
 
-func (c *codegen) writeJumps() {
-	b := c.prog.Bytes()
+func (c *codegen) writeJumps(b []byte) {
 	for i, op := range b {
 		j := i + 1
 		switch vm.Instruction(op) {
diff --git a/pkg/vm/compiler/compiler.go b/pkg/vm/compiler/compiler.go
index 5ead0d34a..cbc4a93be 100644
--- a/pkg/vm/compiler/compiler.go
+++ b/pkg/vm/compiler/compiler.go
@@ -60,7 +60,7 @@ func Compile(r io.Reader) ([]byte, error) {
 		return nil, err
 	}
 
-	return buf.Bytes(), nil
+	return buf, nil
 }
 
 type archive struct {
diff --git a/pkg/vm/compiler/emit.go b/pkg/vm/compiler/emit.go
index 92be632f8..296adea22 100644
--- a/pkg/vm/compiler/emit.go
+++ b/pkg/vm/compiler/emit.go
@@ -1,105 +1,114 @@
 package compiler
 
 import (
-	"bytes"
 	"encoding/binary"
 	"errors"
 	"fmt"
-	"io"
 	"math/big"
 
+	"github.com/CityOfZion/neo-go/pkg/io"
 	"github.com/CityOfZion/neo-go/pkg/util"
 	"github.com/CityOfZion/neo-go/pkg/vm"
 )
 
-func emit(w *bytes.Buffer, instr vm.Instruction, b []byte) error {
-	if err := w.WriteByte(byte(instr)); err != nil {
-		return err
-	}
-	_, err := w.Write(b)
-	return err
+// emit a VM Instruction with data to the given buffer.
+func emit(w *io.BufBinWriter, instr vm.Instruction, b []byte) {
+	w.WriteLE(byte(instr))
+	w.WriteVarBytes(b)
 }
 
-func emitOpcode(w io.ByteWriter, instr vm.Instruction) error {
-	return w.WriteByte(byte(instr))
+// emitOpcode emits a single VM Instruction the given buffer.
+func emitOpcode(w *io.BufBinWriter, instr vm.Instruction) {
+	w.WriteLE(byte(instr))
 }
 
-func emitBool(w io.ByteWriter, ok bool) error {
+// emitBool emits a bool type the given buffer.
+func emitBool(w *io.BufBinWriter, ok bool) {
 	if ok {
-		return emitOpcode(w, vm.PUSHT)
+		emitOpcode(w, vm.PUSHT)
+		return
 	}
-	return emitOpcode(w, vm.PUSHF)
+	emitOpcode(w, vm.PUSHF)
 }
 
-func emitInt(w *bytes.Buffer, i int64) error {
-	if i == -1 {
-		return emitOpcode(w, vm.PUSHM1)
-	}
-	if i == 0 {
-		return emitOpcode(w, vm.PUSHF)
-	}
-	if i > 0 && i < 16 {
+// emitInt emits a int type to the given buffer.
+func emitInt(w *io.BufBinWriter, i int64) {
+	switch {
+	case i == -1:
+		emitOpcode(w, vm.PUSHM1)
+		return
+	case i == 0:
+		emitOpcode(w, vm.PUSHF)
+		return
+	case i > 0 && i < 16:
 		val := vm.Instruction(int(vm.PUSH1) - 1 + int(i))
-		return emitOpcode(w, val)
+		emitOpcode(w, val)
+		return
 	}
 
 	bInt := big.NewInt(i)
 	val := util.ArrayReverse(bInt.Bytes())
-	return emitBytes(w, val)
+	emitBytes(w, val)
 }
 
-func emitString(w *bytes.Buffer, s string) error {
-	return emitBytes(w, []byte(s))
+// emitString emits a string to the given buffer.
+func emitString(w *io.BufBinWriter, s string) {
+	emitBytes(w, []byte(s))
 }
 
-func emitBytes(w *bytes.Buffer, b []byte) error {
-	var (
-		err error
-		n   = len(b)
-	)
+// emitBytes emits a byte array to the given buffer.
+func emitBytes(w *io.BufBinWriter, b []byte) {
+	n := len(b)
 
 	switch {
 	case n <= int(vm.PUSHBYTES75):
-		return emit(w, vm.Instruction(n), b)
+		emit(w, vm.Instruction(n), b)
+		return
 	case n < 0x100:
-		err = emit(w, vm.PUSHDATA1, []byte{byte(n)})
+		emit(w, vm.PUSHDATA1, []byte{byte(n)})
 	case n < 0x10000:
 		buf := make([]byte, 2)
 		binary.LittleEndian.PutUint16(buf, uint16(n))
-		err = emit(w, vm.PUSHDATA2, buf)
+		emit(w, vm.PUSHDATA2, buf)
 	default:
 		buf := make([]byte, 4)
 		binary.LittleEndian.PutUint32(buf, uint32(n))
-		err = emit(w, vm.PUSHDATA4, buf)
+		emit(w, vm.PUSHDATA4, buf)
+		if w.Err != nil {
+			return
+		}
 	}
-	if err != nil {
-		return err
-	}
-	_, err = w.Write(b)
-	return err
+
+	w.WriteBytes(b)
 }
 
-func emitSyscall(w *bytes.Buffer, api string) error {
+// emitSyscall emits the syscall API to the given buffer.
+// Syscall API string cannot be 0.
+func emitSyscall(w *io.BufBinWriter, api string) {
 	if len(api) == 0 {
-		return errors.New("syscall api cannot be of length 0")
+		w.Err = errors.New("syscall api cannot be of length 0")
+		return
 	}
 	buf := make([]byte, len(api)+1)
 	buf[0] = byte(len(api))
 	copy(buf[1:], api)
-	return emit(w, vm.SYSCALL, buf)
+	emit(w, vm.SYSCALL, buf)
 }
 
-func emitCall(w *bytes.Buffer, instr vm.Instruction, label int16) error {
-	return emitJmp(w, instr, label)
+// emitCall emits a call Instruction with label to the given buffer.
+func emitCall(w *io.BufBinWriter, instr vm.Instruction, label int16) {
+	emitJmp(w, instr, label)
 }
 
-func emitJmp(w *bytes.Buffer, instr vm.Instruction, label int16) error {
+// emitJmp emits a jump Instruction along with label to the given buffer.
+func emitJmp(w *io.BufBinWriter, instr vm.Instruction, label int16) {
 	if !isInstrJmp(instr) {
-		return fmt.Errorf("opcode %s is not a jump or call type", instr)
+		w.Err = fmt.Errorf("opcode %s is not a jump or call type", instr)
+		return
 	}
 	buf := make([]byte, 2)
 	binary.LittleEndian.PutUint16(buf, uint16(label))
-	return emit(w, instr, buf)
+	emit(w, instr, buf)
 }
 
 func isInstrJmp(instr vm.Instruction) bool {