diff --git a/google/default.go b/google/default.go
index 96f9a36..5087d84 100644
--- a/google/default.go
+++ b/google/default.go
@@ -18,6 +18,25 @@
 	"golang.org/x/oauth2"
 )
 
+// Credentials holds Google credentials, including "Application Default Credentials".
+// For more details, see:
+// https://developers.google.com/accounts/docs/application-default-credentials
+type Credentials struct {
+	ProjectID   string // may be empty
+	TokenSource oauth2.TokenSource
+
+	// JSON contains the raw bytes from a JSON credentials file.
+	// This field may be nil if authentication is provided by the
+	// environment and not with a credentials file, e.g. when code is
+	// running on Google Cloud Platform.
+	JSON []byte
+}
+
+// DefaultCredentials is the old name of Credentials.
+//
+// Deprecated: use Credentials instead.
+type DefaultCredentials = Credentials
+
 // DefaultClient returns an HTTP Client that uses the
 // DefaultTokenSource to obtain authentication credentials.
 func DefaultClient(ctx context.Context, scope ...string) (*http.Client, error) {
@@ -39,8 +58,23 @@
 	return creds.TokenSource, nil
 }
 
-// Common implementation for FindDefaultCredentials.
-func findDefaultCredentials(ctx context.Context, scopes []string) (*DefaultCredentials, error) {
+// FindDefaultCredentials searches for "Application Default Credentials".
+//
+// It looks for credentials in the following places,
+// preferring the first location found:
+//
+//   1. A JSON file whose path is specified by the
+//      GOOGLE_APPLICATION_CREDENTIALS environment variable.
+//   2. A JSON file in a location known to the gcloud command-line tool.
+//      On Windows, this is %APPDATA%/gcloud/application_default_credentials.json.
+//      On other systems, $HOME/.config/gcloud/application_default_credentials.json.
+//   3. On Google App Engine standard first generation runtimes (<= Go 1.9) it uses
+//      the appengine.AccessToken function.
+//   4. On Google Compute Engine, Google App Engine standard second generation runtimes
+//      (>= Go 1.11), and Google App Engine flexible environment, it fetches
+//      credentials from the metadata server.
+//      (In this final case any provided scopes are ignored.)
+func FindDefaultCredentials(ctx context.Context, scopes ...string) (*Credentials, error) {
 	// First, try the environment variable.
 	const envVar = "GOOGLE_APPLICATION_CREDENTIALS"
 	if filename := os.Getenv(envVar); filename != "" {
@@ -84,8 +118,11 @@
 	return nil, fmt.Errorf("google: could not find default credentials. See %v for more information.", url)
 }
 
-// Common implementation for CredentialsFromJSON.
-func credentialsFromJSON(ctx context.Context, jsonData []byte, scopes []string) (*DefaultCredentials, error) {
+// CredentialsFromJSON obtains Google credentials from a JSON value. The JSON can
+// represent either a Google Developers Console client_credentials.json file (as in
+// ConfigFromJSON) or a Google Developers service account key file (as in
+// JWTConfigFromJSON).
+func CredentialsFromJSON(ctx context.Context, jsonData []byte, scopes ...string) (*Credentials, error) {
 	var f credentialsFile
 	if err := json.Unmarshal(jsonData, &f); err != nil {
 		return nil, err
diff --git a/google/doc_go19.go b/google/doc.go
similarity index 100%
rename from google/doc_go19.go
rename to google/doc.go
diff --git a/google/doc_not_go19.go b/google/doc_not_go19.go
deleted file mode 100644
index 5c3c6e1..0000000
--- a/google/doc_not_go19.go
+++ /dev/null
@@ -1,43 +0,0 @@
-// Copyright 2018 The Go Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-// +build !go1.9
-
-// Package google provides support for making OAuth2 authorized and authenticated
-// HTTP requests to Google APIs. It supports the Web server flow, client-side
-// credentials, service accounts, Google Compute Engine service accounts, and Google
-// App Engine service accounts.
-//
-// A brief overview of the package follows. For more information, please read
-// https://developers.google.com/accounts/docs/OAuth2
-// and
-// https://developers.google.com/accounts/docs/application-default-credentials.
-//
-// OAuth2 Configs
-//
-// Two functions in this package return golang.org/x/oauth2.Config values from Google credential
-// data. Google supports two JSON formats for OAuth2 credentials: one is handled by ConfigFromJSON,
-// the other by JWTConfigFromJSON. The returned Config can be used to obtain a TokenSource or
-// create an http.Client.
-//
-//
-// Credentials
-//
-// The DefaultCredentials type represents Google Application Default Credentials, as
-// well as other forms of credential.
-//
-// Use FindDefaultCredentials to obtain Application Default Credentials.
-// FindDefaultCredentials looks in some well-known places for a credentials file, and
-// will call AppEngineTokenSource or ComputeTokenSource as needed.
-//
-// DefaultClient and DefaultTokenSource are convenience methods. They first call FindDefaultCredentials,
-// then use the credentials to construct an http.Client or an oauth2.TokenSource.
-//
-// Use CredentialsFromJSON to obtain credentials from either of the two JSON
-// formats described in OAuth2 Configs, above. (The DefaultCredentials returned may
-// not be "Application Default Credentials".) The TokenSource in the returned value
-// is the same as the one obtained from the oauth2.Config returned from
-// ConfigFromJSON or JWTConfigFromJSON, but the DefaultCredentials may contain
-// additional information that is useful is some circumstances.
-package google // import "golang.org/x/oauth2/google"
diff --git a/google/go19.go b/google/go19.go
deleted file mode 100644
index 23fe4d8..0000000
--- a/google/go19.go
+++ /dev/null
@@ -1,60 +0,0 @@
-// Copyright 2018 The Go Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-// +build go1.9
-
-package google
-
-import (
-	"context"
-
-	"golang.org/x/oauth2"
-)
-
-// Credentials holds Google credentials, including "Application Default Credentials".
-// For more details, see:
-// https://developers.google.com/accounts/docs/application-default-credentials
-type Credentials struct {
-	ProjectID   string // may be empty
-	TokenSource oauth2.TokenSource
-
-	// JSON contains the raw bytes from a JSON credentials file.
-	// This field may be nil if authentication is provided by the
-	// environment and not with a credentials file, e.g. when code is
-	// running on Google Cloud Platform.
-	JSON []byte
-}
-
-// DefaultCredentials is the old name of Credentials.
-//
-// Deprecated: use Credentials instead.
-type DefaultCredentials = Credentials
-
-// FindDefaultCredentials searches for "Application Default Credentials".
-//
-// It looks for credentials in the following places,
-// preferring the first location found:
-//
-//   1. A JSON file whose path is specified by the
-//      GOOGLE_APPLICATION_CREDENTIALS environment variable.
-//   2. A JSON file in a location known to the gcloud command-line tool.
-//      On Windows, this is %APPDATA%/gcloud/application_default_credentials.json.
-//      On other systems, $HOME/.config/gcloud/application_default_credentials.json.
-//   3. On Google App Engine standard first generation runtimes (<= Go 1.9) it uses
-//      the appengine.AccessToken function.
-//   4. On Google Compute Engine, Google App Engine standard second generation runtimes
-//      (>= Go 1.11), and Google App Engine flexible environment, it fetches
-//      credentials from the metadata server.
-//      (In this final case any provided scopes are ignored.)
-func FindDefaultCredentials(ctx context.Context, scopes ...string) (*Credentials, error) {
-	return findDefaultCredentials(ctx, scopes)
-}
-
-// CredentialsFromJSON obtains Google credentials from a JSON value. The JSON can
-// represent either a Google Developers Console client_credentials.json file (as in
-// ConfigFromJSON) or a Google Developers service account key file (as in
-// JWTConfigFromJSON).
-func CredentialsFromJSON(ctx context.Context, jsonData []byte, scopes ...string) (*Credentials, error) {
-	return credentialsFromJSON(ctx, jsonData, scopes)
-}
diff --git a/google/not_go19.go b/google/not_go19.go
deleted file mode 100644
index f942b32..0000000
--- a/google/not_go19.go
+++ /dev/null
@@ -1,57 +0,0 @@
-// Copyright 2018 The Go Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-// +build !go1.9
-
-package google
-
-import (
-	"context"
-
-	"golang.org/x/oauth2"
-)
-
-// DefaultCredentials holds Google credentials, including "Application Default Credentials".
-// For more details, see:
-// https://developers.google.com/accounts/docs/application-default-credentials
-type DefaultCredentials struct {
-	ProjectID   string // may be empty
-	TokenSource oauth2.TokenSource
-
-	// JSON contains the raw bytes from a JSON credentials file.
-	// This field may be nil if authentication is provided by the
-	// environment and not with a credentials file, e.g. when code is
-	// running on Google Cloud Platform.
-	JSON []byte
-}
-
-// FindDefaultCredentials searches for "Application Default Credentials".
-//
-// It looks for credentials in the following places,
-// preferring the first location found:
-//
-//   1. A JSON file whose path is specified by the
-//      GOOGLE_APPLICATION_CREDENTIALS environment variable.
-//   2. A JSON file in a location known to the gcloud command-line tool.
-//      On Windows, this is %APPDATA%/gcloud/application_default_credentials.json.
-//      On other systems, $HOME/.config/gcloud/application_default_credentials.json.
-//   3. On Google App Engine standard first generation runtimes (<= Go 1.9) it uses
-//      the appengine.AccessToken function.
-//   4. On Google Compute Engine, Google App Engine standard second generation runtimes
-//      (>= Go 1.11), and Google App Engine flexible environment, it fetches
-//      credentials from the metadata server.
-//      (In this final case any provided scopes are ignored.)
-func FindDefaultCredentials(ctx context.Context, scopes ...string) (*DefaultCredentials, error) {
-	return findDefaultCredentials(ctx, scopes)
-}
-
-// CredentialsFromJSON obtains Google credentials from a JSON value. The JSON can
-// represent either a Google Developers Console client_credentials.json file (as in
-// ConfigFromJSON) or a Google Developers service account key file (as in
-// JWTConfigFromJSON).
-//
-// Note: despite the name, the returned credentials may not be Application Default Credentials.
-func CredentialsFromJSON(ctx context.Context, jsonData []byte, scopes ...string) (*DefaultCredentials, error) {
-	return credentialsFromJSON(ctx, jsonData, scopes)
-}