diff --git a/middles/cache.go b/middles/cache.go
index b719d87..b35dc88 100644
--- a/middles/cache.go
+++ b/middles/cache.go
@@ -18,7 +18,7 @@ type CacheHTTP struct {
 func (c *CacheHTTP) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	var ttl time.Duration
 
-	switch c.Env.String() {
+	switch c.Env.Get() {
 	case runtime.Local:
 		ttl = 5 * time.Second
 
diff --git a/middles/cache_test.go b/middles/cache_test.go
index 7ec3d53..64e7c51 100644
--- a/middles/cache_test.go
+++ b/middles/cache_test.go
@@ -16,7 +16,7 @@ func TestCache_ServeHTTP_local(t *testing.T) {
 	run := new(atomic.Bool)
 	c := &CacheHTTP{
 		Env: runtime.Setup(&runtime.Config{
-			Environment: runtime.Local,
+			Environment: "local",
 			Domain:      "example.com",
 		}),
 		H: http.HandlerFunc(func(_ http.ResponseWriter, _ *http.Request) {
@@ -39,7 +39,7 @@ func TestCache_ServeHTTP_staging_css(t *testing.T) {
 	run := new(atomic.Bool)
 	c := &CacheHTTP{
 		Env: runtime.Setup(&runtime.Config{
-			Environment: runtime.Staging,
+			Environment: "staging",
 			Domain:      "example.com",
 		}),
 		H: http.HandlerFunc(func(_ http.ResponseWriter, _ *http.Request) {
@@ -62,7 +62,7 @@ func TestCache_ServeHTTP_staging_txt(t *testing.T) {
 	run := new(atomic.Bool)
 	c := &CacheHTTP{
 		Env: runtime.Setup(&runtime.Config{
-			Environment: runtime.Staging,
+			Environment: "staging",
 			Domain:      "example.com",
 		}),
 		H: http.HandlerFunc(func(_ http.ResponseWriter, _ *http.Request) {
@@ -85,7 +85,7 @@ func TestCache_ServeHTTP_production_css(t *testing.T) {
 	run := new(atomic.Bool)
 	c := &CacheHTTP{
 		Env: runtime.Setup(&runtime.Config{
-			Environment: runtime.Production,
+			Environment: "production",
 			Domain:      "example.com",
 		}),
 		H: http.HandlerFunc(func(_ http.ResponseWriter, _ *http.Request) {
@@ -108,7 +108,7 @@ func TestCache_ServeHTTP_production_txt(t *testing.T) {
 	run := new(atomic.Bool)
 	c := &CacheHTTP{
 		Env: runtime.Setup(&runtime.Config{
-			Environment: runtime.Production,
+			Environment: "production",
 			Domain:      "example.com",
 		}),
 		H: http.HandlerFunc(func(_ http.ResponseWriter, _ *http.Request) {
diff --git a/runtime/environment.go b/runtime/environment.go
index 209bc43..9430d74 100644
--- a/runtime/environment.go
+++ b/runtime/environment.go
@@ -12,25 +12,32 @@ import (
 // LocalPort is the normal port used for local development.
 var LocalPort = 3000
 
+// Platform is one of "local", "staging", or "production".
+type Platform string
+
 func Setup(c *Config) Environment {
 	return Environment{
 		domain:      c.Domain,
-		environment: c.Environment,
+		environment: Platform(c.Environment),
 	}
 }
 
 type Environment struct {
 	domain      string
-	environment string
+	environment Platform
 }
 
 const (
-	Local      = "local"
-	Staging    = "staging"
-	Production = "production"
+	Local      Platform = "local"
+	Staging    Platform = "staging"
+	Production Platform = "production"
 )
 
 func (e Environment) String() string {
+	return string(e.Get())
+}
+
+func (e Environment) Get() Platform {
 	return e.environment
 }
 
diff --git a/runtime/environment_test.go b/runtime/environment_test.go
index 7998714..10fe3ea 100644
--- a/runtime/environment_test.go
+++ b/runtime/environment_test.go
@@ -10,19 +10,19 @@ func TestEnvironment_Validate(t *testing.T) {
 	t.Parallel()
 
 	t.Run("local", func(t *testing.T) {
-		e := Setup(&Config{Environment: Local, Domain: "test.local"})
+		e := Setup(&Config{Environment: "local", Domain: "test.local"})
 		err := e.Validate()
 		must.NoError(t, err)
 	})
 
 	t.Run("staging", func(t *testing.T) {
-		e := Setup(&Config{Environment: Staging, Domain: "example.com"})
+		e := Setup(&Config{Environment: "staging", Domain: "example.com"})
 		err := e.Validate()
 		must.NoError(t, err)
 	})
 
 	t.Run("production", func(t *testing.T) {
-		e := Setup(&Config{Environment: Production, Domain: "example.com"})
+		e := Setup(&Config{Environment: "production", Domain: "example.com"})
 		err := e.Validate()
 		must.NoError(t, err)
 	})
@@ -34,7 +34,7 @@ func TestEnvironment_Validate(t *testing.T) {
 	})
 
 	t.Run("missing domain", func(t *testing.T) {
-		e := Setup(&Config{Environment: Production, Domain: ""})
+		e := Setup(&Config{Environment: "production", Domain: ""})
 		err := e.Validate()
 		must.ErrorContains(t, err, "domain must be set")
 	})
@@ -44,31 +44,31 @@ func TestEnvironment_Canonical(t *testing.T) {
 	t.Parallel()
 
 	t.Run("production", func(t *testing.T) {
-		e := Setup(&Config{Environment: Production, Domain: "example.com"})
+		e := Setup(&Config{Environment: "production", Domain: "example.com"})
 		result := e.Canonical("/about")
 		must.Eq(t, result, "https://example.com/about")
 	})
 
 	t.Run("staging", func(t *testing.T) {
-		e := Setup(&Config{Environment: Staging, Domain: "example.com"})
+		e := Setup(&Config{Environment: "staging", Domain: "example.com"})
 		result := e.Canonical("/about")
 		must.Eq(t, result, "https://stage.example.com/about")
 	})
 
 	t.Run("local", func(t *testing.T) {
-		e := Setup(&Config{Environment: Local, Domain: "example.com"})
+		e := Setup(&Config{Environment: "local", Domain: "example.com"})
 		result := e.Canonical("/about")
 		must.Eq(t, result, "http://localhost:3000/about")
 	})
 
 	t.Run("missing slash", func(t *testing.T) {
-		e := Setup(&Config{Environment: Local, Domain: "example.com"})
+		e := Setup(&Config{Environment: "local", Domain: "example.com"})
 		result := e.Canonical("login")
 		must.Eq(t, result, "http://localhost:3000/login")
 	})
 
 	t.Run("empty", func(t *testing.T) {
-		e := Setup(&Config{Environment: Production, Domain: "example.com"})
+		e := Setup(&Config{Environment: "production", Domain: "example.com"})
 		result := e.Canonical("")
 		must.Eq(t, result, "https://example.com")
 	})