diff --git a/example_test.go b/example_test.go
index d69477e..d7afa38 100644
--- a/example_test.go
+++ b/example_test.go
@@ -56,7 +56,7 @@ func Example_jWTConfig() {
 		// The path to the pem file. If you have a p12 file instead, you
 		// can use `openssl` to export the private key into a pem file.
 		// $ openssl pkcs12 -in key.p12 -out key.pem -nodes
-		PemFilename: "/path/to/pem/file.pem",
+		PEMFilename: "/path/to/pem/file.pem",
 		Scopes:      []string{"SCOPE1", "SCOPE2"},
 	},
 		"https://provider.com/o/oauth2/token")
diff --git a/google/example_test.go b/google/example_test.go
index 2df6d6f..e492507 100644
--- a/google/example_test.go
+++ b/google/example_test.go
@@ -49,10 +49,10 @@ func Example_serviceAccounts() {
 	// Developer Console (https://console.developers.google.com).
 	config, err := google.NewServiceAccountConfig(&oauth2.JWTOptions{
 		Email: "xxx@developer.gserviceaccount.com",
-		// The path to the pem file. If you have a p12 file instead, you
+		// PEMFilename. If you have a p12 file instead, you
 		// can use `openssl` to export the private key into a pem file.
 		// $ openssl pkcs12 -in key.p12 -out key.pem -nodes
-		PemFilename: "/path/to/pem/file.pem",
+		PEMFilename: "/path/to/pem/file.pem",
 		Scopes: []string{
 			"https://www.googleapis.com/auth/bigquery",
 		},
diff --git a/jwt.go b/jwt.go
index d1ea222..82f41c7 100644
--- a/jwt.go
+++ b/jwt.go
@@ -27,21 +27,21 @@ var (
 // JWTOptions represents a OAuth2 client's crendentials to retrieve a
 // Bearer JWT token.
 type JWTOptions struct {
-	// ClientID is the OAuth client identifier used when communicating with
+	// Email is the OAuth client identifier used when communicating with
 	// the configured OAuth provider.
 	Email string `json:"email"`
 
-	// Private key to sign JWS payloads.
+	// PrivateKey is an RSA private key to sign JWS payloads.
 	PrivateKey *rsa.PrivateKey `json:"-"`
 
-	// The path to a pem container that includes your private key.
+	// The path to a PEM container that includes your private key.
 	// If PrivateKey is set, this field is ignored.
 	//
 	// If you have a p12 file instead, you
-	// can use `openssl` to export the private key into a pem file.
+	// can use `openssl` to export the private key into a PEM file.
 	// $ openssl pkcs12 -in key.p12 -out key.pem -nodes
-	// Pem file should contain your private key.
-	PemFilename string `json:"pemfilename"`
+	// PEM file should contain your private key.
+	PEMFilename string `json:"pemfilename"`
 
 	// Scopes identify the level of access being requested.
 	Scopes []string `json:"scopes"`
@@ -57,7 +57,7 @@ func NewJWTConfig(opts *JWTOptions, aud string) (*JWTConfig, error) {
 	if opts.PrivateKey != nil {
 		return &JWTConfig{opts: opts, aud: audURL, key: opts.PrivateKey}, nil
 	}
-	contents, err := ioutil.ReadFile(opts.PemFilename)
+	contents, err := ioutil.ReadFile(opts.PEMFilename)
 	if err != nil {
 		return nil, err
 	}
diff --git a/oauth2.go b/oauth2.go
index 8813e22..6850f3b 100644
--- a/oauth2.go
+++ b/oauth2.go
@@ -61,8 +61,8 @@ type Options struct {
 	// granting (or denying) access.
 	RedirectURL string `json:"redirect_url"`
 
-	// Optional, identifies the level of access being requested.
-	Scopes []string `json:"scopes"`
+	// Scopes optionally specifies a list of requested permission scopes.
+	Scopes []string `json:"scopes,omitempty"`
 
 	// AccessType is an OAuth extension that gets sent as the
 	// "access_type" field in the URL from AuthCodeURL.