diff --git a/authentication_cleartext_password.go b/authentication_cleartext_password.go
index dd82c7a7..1b87a718 100644
--- a/authentication_cleartext_password.go
+++ b/authentication_cleartext_password.go
@@ -2,6 +2,7 @@ package pgproto3
 
 import (
 	"encoding/binary"
+	"encoding/json"
 	"errors"
 
 	"github.com/jackc/pgio"
@@ -37,3 +38,12 @@ func (src *AuthenticationCleartextPassword) Encode(dst []byte) []byte {
 	dst = pgio.AppendUint32(dst, AuthTypeCleartextPassword)
 	return dst
 }
+
+// MarshalJSON implements encoding/json.Marshaler.
+func (src AuthenticationCleartextPassword) MarshalJSON() ([]byte, error) {
+	return json.Marshal(struct {
+		Type string
+	}{
+		Type: "AuthenticationCleartextPassword",
+	})
+}
diff --git a/authentication_md5_password.go b/authentication_md5_password.go
index d505d264..95795b31 100644
--- a/authentication_md5_password.go
+++ b/authentication_md5_password.go
@@ -2,6 +2,7 @@ package pgproto3
 
 import (
 	"encoding/binary"
+	"encoding/json"
 	"errors"
 
 	"github.com/jackc/pgio"
@@ -41,3 +42,33 @@ func (src *AuthenticationMD5Password) Encode(dst []byte) []byte {
 	dst = append(dst, src.Salt[:]...)
 	return dst
 }
+
+// MarshalJSON implements encoding/json.Marshaler.
+func (src AuthenticationMD5Password) MarshalJSON() ([]byte, error) {
+	return json.Marshal(struct {
+		Type string
+		Salt [4]byte
+	}{
+		Type: "AuthenticationMD5Password",
+		Salt: src.Salt,
+	})
+}
+
+// UnmarshalJSON implements encoding/json.Unmarshaler.
+func (dst *AuthenticationMD5Password) UnmarshalJSON(data []byte) error {
+	// Ignore null, like in the main JSON package.
+	if string(data) == "null" {
+		return nil
+	}
+
+	var msg struct {
+		Type string
+		Salt [4]byte
+	}
+	if err := json.Unmarshal(data, &msg); err != nil {
+		return err
+	}
+
+	dst.Salt = msg.Salt
+	return nil
+}
diff --git a/authentication_ok.go b/authentication_ok.go
index 7b13c6e0..ad69b907 100644
--- a/authentication_ok.go
+++ b/authentication_ok.go
@@ -2,6 +2,7 @@ package pgproto3
 
 import (
 	"encoding/binary"
+	"encoding/json"
 	"errors"
 
 	"github.com/jackc/pgio"
@@ -37,3 +38,12 @@ func (src *AuthenticationOk) Encode(dst []byte) []byte {
 	dst = pgio.AppendUint32(dst, AuthTypeOk)
 	return dst
 }
+
+// MarshalJSON implements encoding/json.Marshaler.
+func (src AuthenticationOk) MarshalJSON() ([]byte, error) {
+	return json.Marshal(struct {
+		Type string
+	}{
+		Type: "AuthenticationOK",
+	})
+}
diff --git a/authentication_sasl.go b/authentication_sasl.go
index c57ae32d..d2b09750 100644
--- a/authentication_sasl.go
+++ b/authentication_sasl.go
@@ -3,6 +3,7 @@ package pgproto3
 import (
 	"bytes"
 	"encoding/binary"
+	"encoding/json"
 	"errors"
 
 	"github.com/jackc/pgio"
@@ -58,3 +59,14 @@ func (src *AuthenticationSASL) Encode(dst []byte) []byte {
 
 	return dst
 }
+
+// MarshalJSON implements encoding/json.Marshaler.
+func (src AuthenticationSASL) MarshalJSON() ([]byte, error) {
+	return json.Marshal(struct {
+		Type           string
+		AuthMechanisms []string
+	}{
+		Type:           "AuthenticationSASL",
+		AuthMechanisms: src.AuthMechanisms,
+	})
+}
diff --git a/authentication_sasl_continue.go b/authentication_sasl_continue.go
index 62a16c76..d258065f 100644
--- a/authentication_sasl_continue.go
+++ b/authentication_sasl_continue.go
@@ -48,6 +48,17 @@ func (src *AuthenticationSASLContinue) Encode(dst []byte) []byte {
 	return dst
 }
 
+// MarshalJSON implements encoding/json.Marshaler.
+func (src AuthenticationSASLContinue) MarshalJSON() ([]byte, error) {
+	return json.Marshal(struct {
+		Type string
+		Data string
+	}{
+		Type: "AuthenticationSASLContinue",
+		Data: string(src.Data),
+	})
+}
+
 // UnmarshalJSON implements encoding/json.Unmarshaler.
 func (dst *AuthenticationSASLContinue) UnmarshalJSON(data []byte) error {
 	// Ignore null, like in the main JSON package.
diff --git a/authentication_sasl_final.go b/authentication_sasl_final.go
index de5e454a..6a681d73 100644
--- a/authentication_sasl_final.go
+++ b/authentication_sasl_final.go
@@ -48,6 +48,17 @@ func (src *AuthenticationSASLFinal) Encode(dst []byte) []byte {
 	return dst
 }
 
+// MarshalJSON implements encoding/json.Unmarshaler.
+func (src AuthenticationSASLFinal) MarshalJSON() ([]byte, error) {
+	return json.Marshal(struct {
+		Type string
+		Data string
+	}{
+		Type: "AuthenticationSASLFinal",
+		Data: string(src.Data),
+	})
+}
+
 // UnmarshalJSON implements encoding/json.Unmarshaler.
 func (dst *AuthenticationSASLFinal) UnmarshalJSON(data []byte) error {
 	// Ignore null, like in the main JSON package.
diff --git a/error_response.go b/error_response.go
index 4eb0a196..ec51e019 100644
--- a/error_response.go
+++ b/error_response.go
@@ -3,6 +3,7 @@ package pgproto3
 import (
 	"bytes"
 	"encoding/binary"
+	"encoding/json"
 	"strconv"
 )
 
@@ -225,3 +226,109 @@ func (src *ErrorResponse) marshalBinary(typeByte byte) []byte {
 
 	return buf.Bytes()
 }
+
+// MarshalJSON implements encoding/json.Marshaler.
+func (src ErrorResponse) MarshalJSON() ([]byte, error) {
+	return json.Marshal(struct {
+		Type                string
+		Severity            string
+		SeverityUnlocalized string // only in 9.6 and greater
+		Code                string
+		Message             string
+		Detail              string
+		Hint                string
+		Position            int32
+		InternalPosition    int32
+		InternalQuery       string
+		Where               string
+		SchemaName          string
+		TableName           string
+		ColumnName          string
+		DataTypeName        string
+		ConstraintName      string
+		File                string
+		Line                int32
+		Routine             string
+
+		UnknownFields map[byte]string
+	}{
+		Type:                "ErrorResponse",
+		Severity:            src.Severity,
+		SeverityUnlocalized: src.SeverityUnlocalized,
+		Code:                src.Code,
+		Message:             src.Message,
+		Detail:              src.Detail,
+		Hint:                src.Hint,
+		Position:            src.Position,
+		InternalPosition:    src.InternalPosition,
+		InternalQuery:       src.InternalQuery,
+		Where:               src.Where,
+		SchemaName:          src.SchemaName,
+		TableName:           src.TableName,
+		ColumnName:          src.ColumnName,
+		DataTypeName:        src.DataTypeName,
+		ConstraintName:      src.ConstraintName,
+		File:                src.File,
+		Line:                src.Line,
+		Routine:             src.Routine,
+		UnknownFields:       src.UnknownFields,
+	})
+}
+
+// UnmarshalJSON implements encoding/json.Unmarshaler.
+func (dst *ErrorResponse) UnmarshalJSON(data []byte) error {
+	// Ignore null, like in the main JSON package.
+	if string(data) == "null" {
+		return nil
+	}
+
+	var msg struct {
+		Type                string
+		Severity            string
+		SeverityUnlocalized string // only in 9.6 and greater
+		Code                string
+		Message             string
+		Detail              string
+		Hint                string
+		Position            int32
+		InternalPosition    int32
+		InternalQuery       string
+		Where               string
+		SchemaName          string
+		TableName           string
+		ColumnName          string
+		DataTypeName        string
+		ConstraintName      string
+		File                string
+		Line                int32
+		Routine             string
+
+		UnknownFields map[byte]string
+	}
+	if err := json.Unmarshal(data, &msg); err != nil {
+		return err
+	}
+
+	dst.Severity = msg.Severity
+	dst.SeverityUnlocalized = msg.SeverityUnlocalized
+	dst.Code = msg.Code
+	dst.Message = msg.Message
+	dst.Detail = msg.Detail
+	dst.Hint = msg.Hint
+	dst.Position = msg.Position
+	dst.InternalPosition = msg.InternalPosition
+	dst.InternalQuery = msg.InternalQuery
+	dst.Where = msg.Where
+	dst.SchemaName = msg.SchemaName
+	dst.TableName = msg.TableName
+	dst.ColumnName = msg.ColumnName
+	dst.DataTypeName = msg.DataTypeName
+	dst.ConstraintName = msg.ConstraintName
+	dst.File = msg.File
+	dst.Line = msg.Line
+	dst.Routine = msg.Routine
+
+	dst.UnknownFields = msg.UnknownFields
+
+	return nil
+}
diff --git a/json_test.go b/json_test.go
index c73807ab..eab26252 100644
--- a/json_test.go
+++ b/json_test.go
@@ -23,9 +23,9 @@ func TestJSONUnmarshalAuthenticationMD5Password(t *testing.T) {
 }
 
 func TestJSONUnmarshalAuthenticationSASL(t *testing.T) {
-	data := []byte(`{"Type":"AuthenticationSASL", "AuthMechanisms":[]}`)
+	data := []byte(`{"Type":"AuthenticationSASL","AuthMechanisms":["SCRAM-SHA-256"]}`)
 	want := AuthenticationSASL{
-		AuthMechanisms: []string{},
+		[]string{"SCRAM-SHA-256"},
 	}
 
 	var got AuthenticationSASL
@@ -38,9 +38,9 @@ func TestJSONUnmarshalAuthenticationSASL(t *testing.T) {
 }
 
 func TestJSONUnmarshalAuthenticationSASLContinue(t *testing.T) {
-	data := []byte(`{"Type":"AuthenticationSASLContinue"}`)
+	data := []byte(`{"Type":"AuthenticationSASLContinue", "Data":"1"}`)
 	want := AuthenticationSASLContinue{
-		Data: []byte{},
+		Data: []byte{'1'},
 	}
 
 	var got AuthenticationSASLContinue
@@ -53,9 +53,9 @@ func TestJSONUnmarshalAuthenticationSASLContinue(t *testing.T) {
 }
 
 func TestJSONUnmarshalAuthenticationSASLFinal(t *testing.T) {
-	data := []byte(`{"Type":"AuthenticationSASLFinal"}`)
+	data := []byte(`{"Type":"AuthenticationSASLFinal", "Data":"1"}`)
 	want := AuthenticationSASLFinal{
-		Data: []byte{},
+		Data: []byte{'1'},
 	}
 
 	var got AuthenticationSASLFinal
@@ -463,8 +463,11 @@ func TestJSONUnmarshalQuery(t *testing.T) {
 }
 
 func TestJSONUnmarshalSASLInitialResponse(t *testing.T) {
-	data := []byte(`{"Type":"SASLInitialResponse"}`)
-	want := SASLInitialResponse{}
+	data := []byte(`{"Type":"SASLInitialResponse", "AuthMechanism":"SCRAM-SHA-256", "Data": "6D"}`)
+	want := SASLInitialResponse{
+		AuthMechanism: "SCRAM-SHA-256",
+		Data:          []byte{109},
+	}
 
 	var got SASLInitialResponse
 	if err := json.Unmarshal(data, &got); err != nil {
@@ -506,3 +509,64 @@ func TestJSONUnmarshalStartupMessage(t *testing.T) {
 		t.Error("unmarshaled StartupMessage struct doesn't match expected value")
 	}
 }
+
+func TestAuthenticationOK(t *testing.T) {
+	data := []byte(`{"Type":"AuthenticationOK"}`)
+	want := AuthenticationOk{}
+
+	var got AuthenticationOk
+	if err := json.Unmarshal(data, &got); err != nil {
+		t.Errorf("cannot JSON unmarshal %v", err)
+	}
+	if !reflect.DeepEqual(got, want) {
+		t.Error("unmarshaled AuthenticationOK struct doesn't match expected value")
+	}
+}
+
+func TestAuthenticationCleartextPassword(t *testing.T) {
+	data := []byte(`{"Type":"AuthenticationCleartextPassword"}`)
+	want := AuthenticationCleartextPassword{}
+
+	var got AuthenticationCleartextPassword
+	if err := json.Unmarshal(data, &got); err != nil {
+		t.Errorf("cannot JSON unmarshal %v", err)
+	}
+	if !reflect.DeepEqual(got, want) {
+		t.Error("unmarshaled AuthenticationCleartextPassword struct doesn't match expected value")
+	}
+}
+
+func TestAuthenticationMD5Password(t *testing.T) {
+	data := []byte(`{"Type":"AuthenticationMD5Password","Salt":[1,2,3,4]}`)
+	want := AuthenticationMD5Password{
+		Salt: [4]byte{1, 2, 3, 4},
+	}
+
+	var got AuthenticationMD5Password
+	if err := json.Unmarshal(data, &got); err != nil {
+		t.Errorf("cannot JSON unmarshal %v", err)
+	}
+	if !reflect.DeepEqual(got, want) {
+		t.Error("unmarshaled AuthenticationMD5Password struct doesn't match expected value")
+	}
+}
+
+func TestErrorResponse(t *testing.T) {
+	data := []byte(`{"Type":"ErrorResponse","UnknownFields":{"112":"foo"},"Code": "Fail","Position":1,"Message":"this is an error"}`)
+	want := ErrorResponse{
+		UnknownFields: map[byte]string{
+			'p': "foo",
+		},
+		Code:     "Fail",
+		Position: 1,
+		Message:  "this is an error",
+	}
+
+	var got ErrorResponse
+	if err := json.Unmarshal(data, &got); err != nil {
+		t.Errorf("cannot JSON unmarshal %v", err)
+	}
+	if !reflect.DeepEqual(got, want) {
+		t.Error("unmarshaled ErrorResponse struct doesn't match expected value")
+	}
+}