diff --git a/xdr2/decode.go b/xdr2/decode.go
index eea39cf..6a8712a 100644
--- a/xdr2/decode.go
+++ b/xdr2/decode.go
@@ -518,7 +518,7 @@ func (d *Decoder) decodeStruct(v reflect.Value) (int, error) {
 			hasopt, n2, err := d.DecodeBool()
 			n += n2
 			if err != nil {
-				return n2, err
+				return n, err
 			}
 			if !hasopt {
 				continue
diff --git a/xdr2/decode_test.go b/xdr2/decode_test.go
index 1d34497..c7c2641 100644
--- a/xdr2/decode_test.go
+++ b/xdr2/decode_test.go
@@ -399,6 +399,9 @@ func TestUnmarshal(t *testing.T) {
 		{[]byte{0x00, 0x00, 0x00, 0x01, 0x00, 0x00, 0x00, 0x01, 0x00, 0x00, 0x00, 0x02, 0x00, 0x00, 0x00, 0x00},
 			optionalDataStruct{1, &optionalDataStruct{2, nil}},
 			16, nil},
+		{[]byte{0x00, 0x00, 0x00, 0x01, 0x00, 0x00, 0x00},
+			optionalDataStruct{1, nil},
+			7, &UnmarshalError{ErrorCode: ErrIO}},
 		{[]byte{0x00, 0x00, 0x00, 0x01, 0x00, 0x00, 0x00, 0x00},
 			invalidOptionalDataStruct{},
 			0, &UnmarshalError{ErrorCode: ErrBadOptional}},
diff --git a/xdr2/encode.go b/xdr2/encode.go
index 6813036..73a2ff0 100644
--- a/xdr2/encode.go
+++ b/xdr2/encode.go
@@ -467,7 +467,7 @@ func (enc *Encoder) encodeStruct(v reflect.Value) (int, error) {
 			n2, err := enc.EncodeBool(hasopt)
 			n += n2
 			if err != nil {
-				return n2, err
+				return n, err
 			}
 			if !hasopt {
 				continue
diff --git a/xdr2/encode_test.go b/xdr2/encode_test.go
index 25e6096..7e59f30 100644
--- a/xdr2/encode_test.go
+++ b/xdr2/encode_test.go
@@ -327,8 +327,12 @@ func TestMarshal(t *testing.T) {
 		{optionalDataStruct{1, &optionalDataStruct{2, nil}},
 			[]byte{0x00, 0x00, 0x00, 0x01, 0x00, 0x00, 0x00, 0x01, 0x00, 0x00, 0x00, 0x02, 0x00, 0x00, 0x00, 0x00},
 			16, nil},
+		{optionalDataStruct{1, nil},
+			[]uint8{0x00, 0x00, 0x00, 0x01, 0x00, 0x00, 0x00},
+			7, &MarshalError{ErrorCode: ErrIO}},
 		{invalidOptionalDataStruct{1},
-			[]byte{}, 0, &MarshalError{ErrorCode: ErrBadOptional}},
+			[]byte{},
+			0, &MarshalError{ErrorCode: ErrBadOptional}},
 
 		// Expected errors
 		{nilInterface, []byte{}, 0, &MarshalError{ErrorCode: ErrNilInterface}},