diff --git a/encoding/ascii.go b/encoding/ascii.go
index 2557e43..7f4b083 100644
--- a/encoding/ascii.go
+++ b/encoding/ascii.go
@@ -4,10 +4,11 @@ import "bytes"
 
 type ASCIICoder struct{}
 
-func (c *ASCIICoder) Encode(s string, buf *bytes.Buffer) {
+func (c *ASCIICoder) Encode(s string, buf *bytes.Buffer) error {
 	buf.WriteString(s)
+	return nil
 }
 
-func (c *ASCIICoder) Decode(buf *bytes.Buffer) string {
-	return buf.String()
+func (c *ASCIICoder) Decode(buf *bytes.Buffer) (string, error) {
+	return buf.String(), nil
 }
diff --git a/encoding/ascii_test.go b/encoding/ascii_test.go
index d28f93b..bea47c9 100644
--- a/encoding/ascii_test.go
+++ b/encoding/ascii_test.go
@@ -11,7 +11,11 @@ func TestASCIIEncodeSimpleASCIIString(t *testing.T) {
 	input := "Hello, World!"
 
 	expected := []byte{72, 101, 108, 108, 111, 44, 32, 87, 111, 114, 108, 100, 33}
-	coder.Encode(input, &buf)
+	err := coder.Encode(input, &buf)
+
+	if err != nil {
+		t.Errorf("Expected no error, but got %v", err)
+	}
 
 	if !bytes.Equal(buf.Bytes(), expected) {
 		t.Errorf("Expected %v, but got %v", expected, buf.Bytes())
@@ -25,7 +29,11 @@ func TestASCIIDecodeSimpleASCIIString(t *testing.T) {
 
 	expected := "Hello, World!"
 	buf.Write(input)
-	output := coder.Decode(&buf)
+	output, err := coder.Decode(&buf)
+
+	if err != nil {
+		t.Errorf("Expected no error, but got %v", err)
+	}
 
 	if output != expected {
 		t.Errorf("Expected %v, but got %v", expected, output)
@@ -38,7 +46,11 @@ func TestASCIIEncodeEmptyString(t *testing.T) {
 	input := ""
 
 	expected := []byte{}
-	coder.Encode(input, &buf)
+	err := coder.Encode(input, &buf)
+
+	if err != nil {
+		t.Errorf("Expected no error, but got %v", err)
+	}
 
 	if !bytes.Equal(buf.Bytes(), expected) {
 		t.Errorf("Expected %v, but got %v", expected, buf.Bytes())
@@ -50,7 +62,11 @@ func TestASCIIDecodeEmptyString(t *testing.T) {
 	buf := bytes.NewBuffer([]byte{})
 
 	expected := ""
-	output := coder.Decode(buf)
+	output, err := coder.Decode(buf)
+
+	if err != nil {
+		t.Errorf("Expected no error, but got %v", err)
+	}
 
 	if output != expected {
 		t.Errorf("Expected %v, but got %v", expected, output)
diff --git a/encoding/coder.go b/encoding/coder.go
index 7f2c39b..3a1ac50 100644
--- a/encoding/coder.go
+++ b/encoding/coder.go
@@ -3,6 +3,6 @@ package encoding
 import "bytes"
 
 type Coder interface {
-	Encode(s string, buf *bytes.Buffer)
-	Decode(buf *bytes.Buffer) string
+	Encode(s string, buf *bytes.Buffer) error
+	Decode(buf *bytes.Buffer) (string, error)
 }
\ No newline at end of file