diff --git a/config/http_config.go b/config/http_config.go
index eedb2169..063edde0 100644
--- a/config/http_config.go
+++ b/config/http_config.go
@@ -80,12 +80,41 @@ func (tv *TLSVersion) UnmarshalYAML(unmarshal func(interface{}) error) error {
 }
 
 func (tv *TLSVersion) MarshalYAML() (interface{}, error) {
+	if tv != nil || *tv == 0 {
+		return []byte("null"), nil
+	}
 	for s, v := range TLSVersions {
 		if *tv == v {
 			return s, nil
 		}
 	}
-	return fmt.Sprintf("%v", tv), nil
+	return nil, fmt.Errorf("unknown TLS version: %d", tv)
+}
+
+// MarshalJSON implements the json.Unmarshaler interface for TLSVersion.
+func (tv *TLSVersion) UnmarshalJSON(data []byte) error {
+	var s string
+	if err := json.Unmarshal(data, &s); err != nil {
+		return err
+	}
+	if v, ok := TLSVersions[s]; ok {
+		*tv = v
+		return nil
+	}
+	return fmt.Errorf("unknown TLS version: %s", s)
+}
+
+// MarshalJSON implements the json.Marshaler interface for TLSVersion.
+func (tv *TLSVersion) MarshalJSON() ([]byte, error) {
+	if tv != nil || *tv == 0 {
+		return []byte("null"), nil
+	}
+	for s, v := range TLSVersions {
+		if *tv == v {
+			return []byte(s), nil
+		}
+	}
+	return nil, fmt.Errorf("unknown TLS version: %d", tv)
 }
 
 // BasicAuth contains basic HTTP authentication credentials.
@@ -751,7 +780,7 @@ type TLSConfig struct {
 	// Disable target certificate validation.
 	InsecureSkipVerify bool `yaml:"insecure_skip_verify" json:"insecure_skip_verify"`
 	// Minimum TLS version.
-	MinVersion TLSVersion `yaml:"min_version,omitempty"`
+	MinVersion TLSVersion `yaml:"min_version,omitempty" json:"min_version,omitempty"`
 }
 
 // SetDirectory joins any relative file paths with dir.
diff --git a/config/testdata/tls_config.empty.good.json b/config/testdata/tls_config.empty.good.json
new file mode 100644
index 00000000..0967ef42
--- /dev/null
+++ b/config/testdata/tls_config.empty.good.json
@@ -0,0 +1 @@
+{}
diff --git a/config/testdata/tls_config.insecure.good.json b/config/testdata/tls_config.insecure.good.json
new file mode 100644
index 00000000..57fcd98f
--- /dev/null
+++ b/config/testdata/tls_config.insecure.good.json
@@ -0,0 +1 @@
+{"insecure_skip_verify": true}
diff --git a/config/testdata/tls_config.tlsversion.good.json b/config/testdata/tls_config.tlsversion.good.json
new file mode 100644
index 00000000..c8d41cde
--- /dev/null
+++ b/config/testdata/tls_config.tlsversion.good.json
@@ -0,0 +1 @@
+{"min_version": "TLS11"}
diff --git a/config/tls_config_test.go b/config/tls_config_test.go
index b164a2f3..c759b86e 100644
--- a/config/tls_config_test.go
+++ b/config/tls_config_test.go
@@ -14,23 +14,39 @@
 package config
 
 import (
+	"bytes"
 	"crypto/tls"
+	"fmt"
 	"io/ioutil"
+	"path/filepath"
 	"reflect"
 	"testing"
 
+	"encoding/json"
+
 	"gopkg.in/yaml.v2"
 )
 
-// LoadTLSConfig parses the given YAML file into a tls.Config.
+// LoadTLSConfig parses the given file into a tls.Config.
 func LoadTLSConfig(filename string) (*tls.Config, error) {
 	content, err := ioutil.ReadFile(filename)
 	if err != nil {
 		return nil, err
 	}
 	cfg := TLSConfig{}
-	if err = yaml.UnmarshalStrict(content, &cfg); err != nil {
-		return nil, err
+	switch filepath.Ext(filename) {
+	case ".yml":
+		if err = yaml.UnmarshalStrict(content, &cfg); err != nil {
+			return nil, err
+		}
+	case ".json":
+		decoder := json.NewDecoder(bytes.NewReader(content))
+		decoder.DisallowUnknownFields()
+		if err = decoder.Decode(&cfg); err != nil {
+			return nil, err
+		}
+	default:
+		return nil, fmt.Errorf("Unknown extension: %s", filepath.Ext(filename))
 	}
 	return NewTLSConfig(&cfg)
 }
@@ -39,6 +55,16 @@ var expectedTLSConfigs = []struct {
 	filename string
 	config   *tls.Config
 }{
+	{
+		filename: "tls_config.empty.good.json",
+		config:   &tls.Config{},
+	}, {
+		filename: "tls_config.insecure.good.json",
+		config:   &tls.Config{InsecureSkipVerify: true},
+	}, {
+		filename: "tls_config.tlsversion.good.json",
+		config:   &tls.Config{MinVersion: tls.VersionTLS11},
+	},
 	{
 		filename: "tls_config.empty.good.yml",
 		config:   &tls.Config{},
@@ -55,7 +81,7 @@ func TestValidTLSConfig(t *testing.T) {
 	for _, cfg := range expectedTLSConfigs {
 		got, err := LoadTLSConfig("testdata/" + cfg.filename)
 		if err != nil {
-			t.Errorf("Error parsing %s: %s", cfg.filename, err)
+			t.Fatalf("Error parsing %s: %s", cfg.filename, err)
 		}
 		// non-nil functions are never equal.
 		got.GetClientCertificate = nil