diff --git a/includes/class-amp-theme-support.php b/includes/class-amp-theme-support.php
index 0370f824035..e03466ac7f5 100644
--- a/includes/class-amp-theme-support.php
+++ b/includes/class-amp-theme-support.php
@@ -318,7 +318,8 @@ public static function read_theme_support() {
 				);
 			}
 
-			$is_paired = ! empty( $args[ self::PAIRED_FLAG ] );
+			// See amp_is_canonical().
+			$is_paired = isset( $args[ self::PAIRED_FLAG ] ) ? $args[ self::PAIRED_FLAG ] : ! empty( $args['template_dir'] );
 
 			self::$support_added_via_theme  = $is_paired ? self::TRANSITIONAL_MODE_SLUG : self::STANDARD_MODE_SLUG;
 			self::$support_added_via_option = $theme_support_option;
diff --git a/includes/options/class-amp-options-manager.php b/includes/options/class-amp-options-manager.php
index 5943f580a63..3c23da302a6 100644
--- a/includes/options/class-amp-options-manager.php
+++ b/includes/options/class-amp-options-manager.php
@@ -126,9 +126,8 @@ public static function get_options() {
 
 		$defaults['enable_response_caching'] = wp_using_ext_object_cache();
 
-		$args = AMP_Theme_Support::get_theme_support_args();
-		if ( false !== $args ) {
-			$defaults['theme_support'] = empty( $args[ AMP_Theme_Support::PAIRED_FLAG ] ) ? AMP_Theme_Support::STANDARD_MODE_SLUG : AMP_Theme_Support::TRANSITIONAL_MODE_SLUG;
+		if ( current_theme_supports( 'amp' ) ) {
+			$defaults['theme_support'] = amp_is_canonical() ? AMP_Theme_Support::STANDARD_MODE_SLUG : AMP_Theme_Support::TRANSITIONAL_MODE_SLUG;
 		}
 
 		$options = array_merge( $defaults, $options );
diff --git a/tests/php/test-amp-helper-functions.php b/tests/php/test-amp-helper-functions.php
index 873af10b55e..bca1566cba1 100644
--- a/tests/php/test-amp-helper-functions.php
+++ b/tests/php/test-amp-helper-functions.php
@@ -269,15 +269,15 @@ public function test_amp_add_frontend_actions() {
 	public function get_amphtml_urls() {
 		$post_id = self::factory()->post->create();
 		return [
-			'home' => [
+			'is_home' => [
 				home_url( '/' ),
 				add_query_arg( amp_get_slug(), '', home_url( '/' ) ),
 			],
-			'404'  => [
+			'is_404'  => [
 				home_url( '/no-existe/' ),
 				add_query_arg( amp_get_slug(), '', home_url( '/no-existe/' ) ),
 			],
-			'post' => [
+			'is_post' => [
 				get_permalink( $post_id ),
 				amp_get_permalink( $post_id ),
 			],
@@ -292,8 +292,45 @@ public function get_amphtml_urls() {
 	 * @param string $canonical_url Canonical URL.
 	 * @param string $amphtml_url   The amphtml URL.
 	 */
-	public function test_amp_add_amphtml_link( $canonical_url, $amphtml_url ) {
+	public function test_amp_add_amphtml_link_reader_mode( $canonical_url, $amphtml_url ) {
+		$this->assertFalse( current_theme_supports( AMP_Theme_Support::SLUG ) );
+		$this->assertFalse( amp_is_canonical() );
+		$get_amp_html_link = static function() {
+			return get_echo( 'amp_add_amphtml_link' );
+		};
+
+		$assert_amphtml_link_present = function() use ( $amphtml_url, $get_amp_html_link ) {
+			$this->assertEquals(
+				sprintf( '<link rel="amphtml" href="%s">', esc_url( $amphtml_url ) ),
+				$get_amp_html_link()
+			);
+		};
+
+		$this->go_to( $canonical_url );
+		$assert_amphtml_link_present();
+
+		// Make sure adding the filter hides the amphtml link.
+		add_filter( 'amp_frontend_show_canonical', '__return_false' );
+		$this->assertEmpty( $get_amp_html_link() );
+		remove_filter( 'amp_frontend_show_canonical', '__return_false' );
+		$assert_amphtml_link_present();
+	}
+
+	/**
+	 * Adding link when theme support in transitional mode.
+	 *
+	 * @dataProvider get_amphtml_urls
+	 * @covers ::amp_add_amphtml_link()
+	 * @param string $canonical_url Canonical URL.
+	 * @param string $amphtml_url   The amphtml URL.
+	 */
+	public function test_amp_add_amphtml_link_transitional_mode( $canonical_url, $amphtml_url ) {
+		AMP_Options_Manager::update_option( 'theme_support', AMP_Theme_Support::TRANSITIONAL_MODE_SLUG );
 		AMP_Options_Manager::update_option( 'auto_accept_sanitization', false );
+		AMP_Theme_Support::read_theme_support();
+		AMP_Theme_Support::init();
+		$this->assertTrue( current_theme_supports( AMP_Theme_Support::SLUG ) );
+		$this->assertFalse( amp_is_canonical() );
 
 		$get_amp_html_link = static function() {
 			return get_echo( 'amp_add_amphtml_link' );
@@ -316,15 +353,6 @@ public function test_amp_add_amphtml_link( $canonical_url, $amphtml_url ) {
 		$assert_amphtml_link_present();
 
 		// Make sure that the link is not provided when there are validation errors associated with the URL.
-		add_theme_support(
-			AMP_Theme_Support::SLUG,
-			[
-				'template_dir' => './',
-			]
-		);
-		AMP_Options_Manager::update_option( 'theme_support', AMP_Theme_Support::STANDARD_MODE_SLUG );
-		AMP_Theme_Support::read_theme_support();
-		AMP_Theme_Support::init();
 		$invalid_url_post_id = AMP_Validated_URL_Post_Type::store_validation_errors(
 			[
 				[ 'code' => 'foo' ],
@@ -332,10 +360,12 @@ public function test_amp_add_amphtml_link( $canonical_url, $amphtml_url ) {
 			$canonical_url
 		);
 		$this->assertNotInstanceOf( 'WP_Error', $invalid_url_post_id );
+		$this->assertContains( '<!--', $get_amp_html_link() );
+		$this->assertTrue( AMP_Theme_Support::is_paired_available() );
 
 		// Allow the URL when the errors are forcibly sanitized.
-		$this->assertContains( '<!--', $get_amp_html_link() );
 		add_filter( 'amp_validation_error_sanitized', '__return_true' );
+		$this->assertTrue( AMP_Theme_Support::is_paired_available() );
 		$assert_amphtml_link_present();
 	}
 
diff --git a/tests/php/test-amp.php b/tests/php/test-amp.php
index 2ebc715a515..5ac8bc7ad0f 100644
--- a/tests/php/test-amp.php
+++ b/tests/php/test-amp.php
@@ -18,49 +18,80 @@ public function tearDown() {
 		remove_theme_support( AMP_Theme_Support::SLUG );
 	}
 
+	/**
+	 * Get data for test_amp_is_canonical.
+	 *
+	 * @return array
+	 */
+	public function get_amp_is_canonical_test_data() {
+		return [
+			'default'                     => [
+				null,
+				false,
+				null,
+			],
+			'no_args'                     => [
+				[],
+				true,
+				AMP_Theme_Support::STANDARD_MODE_SLUG,
+			],
+			'paired_implied'              => [
+				[
+					'template_dir' => 'amp-templates',
+				],
+				false,
+				AMP_Theme_Support::TRANSITIONAL_MODE_SLUG,
+			],
+			'paired_with_template_dir'    => [
+				[
+					AMP_Theme_Support::PAIRED_FLAG => true,
+					'template_dir'                 => 'amp-templates',
+				],
+				false,
+				AMP_Theme_Support::TRANSITIONAL_MODE_SLUG,
+			],
+			'canonical_with_template_dir' => [
+				[
+					// This should be a rare scenario, as standard mode should mean no separate templates.
+					AMP_Theme_Support::PAIRED_FLAG => false,
+					'template_dir'                 => 'amp-templates',
+				],
+				true,
+				AMP_Theme_Support::STANDARD_MODE_SLUG,
+			],
+			'paired_without_template_dir' => [
+				[
+					AMP_Theme_Support::PAIRED_FLAG => true,
+				],
+				false,
+				AMP_Theme_Support::TRANSITIONAL_MODE_SLUG,
+			],
+		];
+	}
+
 	/**
 	 * Test amp_is_canonical().
 	 *
+	 * @dataProvider get_amp_is_canonical_test_data
 	 * @covers ::amp_is_canonical()
+	 * @covers AMP_Theme_Support::get_support_mode_added_via_theme()
+	 * @covers AMP_Theme_Support::read_theme_support()
+	 * @param mixed  $theme_support_args Theme support args.
+	 * @param bool   $is_canonical       Whether canonical.
+	 * @param string $expected_mode      Expected mode.
 	 */
-	public function test_amp_is_canonical() {
+	public function test_amp_is_canonical( $theme_support_args, $is_canonical, $expected_mode ) {
 		remove_theme_support( AMP_Theme_Support::SLUG );
-		$this->assertFalse( amp_is_canonical() );
-
-		add_theme_support( AMP_Theme_Support::SLUG );
-		$this->assertTrue( amp_is_canonical() );
-
-		add_theme_support(
-			AMP_Theme_Support::SLUG,
-			[
-				'template_dir' => 'amp-templates',
-			]
-		);
-		$this->assertFalse( amp_is_canonical() );
-
-		add_theme_support(
-			AMP_Theme_Support::SLUG,
-			[
-				AMP_Theme_Support::PAIRED_FLAG => false,
-				'template_dir'                 => 'amp-templates',
-			]
-		);
-		$this->assertTrue( amp_is_canonical() );
-
-		add_theme_support(
-			AMP_Theme_Support::SLUG,
-			[
-				AMP_Theme_Support::PAIRED_FLAG => true,
-			]
-		);
-		$this->assertFalse( amp_is_canonical() );
-
-		add_theme_support(
-			AMP_Theme_Support::SLUG,
-			[
-				'custom_prop' => 'something',
-			]
-		);
-		$this->assertTrue( amp_is_canonical() );
+		delete_option( AMP_Options_Manager::OPTION_NAME );
+		if ( isset( $theme_support_args ) ) {
+			if ( is_array( $theme_support_args ) ) {
+				add_theme_support( AMP_Theme_Support::SLUG, $theme_support_args );
+			} else {
+				add_theme_support( AMP_Theme_Support::SLUG );
+			}
+		}
+		AMP_Theme_Support::read_theme_support();
+		$this->assertSame( $expected_mode, AMP_Theme_Support::get_support_mode_added_via_theme() );
+		$this->assertSame( $is_canonical, amp_is_canonical() );
 	}
 }
diff --git a/tests/php/test-class-amp-options-manager.php b/tests/php/test-class-amp-options-manager.php
index f81ba2835bb..e1e62092841 100644
--- a/tests/php/test-class-amp-options-manager.php
+++ b/tests/php/test-class-amp-options-manager.php
@@ -269,6 +269,95 @@ public function test_get_and_set_options() {
 		}
 	}
 
+
+	public function get_test_get_options_defaults_data() {
+		return [
+			'reader'                               => [
+				null,
+				AMP_Theme_Support::READER_MODE_SLUG,
+			],
+			'transitional_without_template_dir'    => [
+				[
+					'paired' => true,
+				],
+				AMP_Theme_Support::TRANSITIONAL_MODE_SLUG,
+			],
+			'transitional_implied_by_template_dir' => [
+				[
+					'template_dir' => 'amp',
+				],
+				AMP_Theme_Support::TRANSITIONAL_MODE_SLUG,
+			],
+			'standard_paired_false'                => [
+				[
+					'paired' => false,
+				],
+				AMP_Theme_Support::STANDARD_MODE_SLUG,
+			],
+			'standard_paired_false'                => [
+				[
+					'paired' => false,
+				],
+				AMP_Theme_Support::STANDARD_MODE_SLUG,
+			],
+			'standard_no_args'                     => [
+				[],
+				AMP_Theme_Support::STANDARD_MODE_SLUG,
+			],
+			'standard_via_native'                  => [
+				null,
+				AMP_Theme_Support::STANDARD_MODE_SLUG,
+				[
+					'theme_support' => 'native',
+				],
+			],
+			'standard_via_native'                  => [
+				null,
+				AMP_Theme_Support::TRANSITIONAL_MODE_SLUG,
+				[
+					'theme_support' => 'paired',
+				],
+			],
+			'standard_upon_upgrade'                => [
+				[
+					'paired' => false,
+				],
+				AMP_Theme_Support::STANDARD_MODE_SLUG,
+				[
+					'theme_support' => 'disabled',
+				],
+			],
+			'transitional_upon_upgrade'            => [
+				[
+					'paired' => true,
+				],
+				AMP_Theme_Support::TRANSITIONAL_MODE_SLUG,
+				[
+					'theme_support' => 'disabled',
+				],
+			],
+		];
+	}
+
+	/**
+	 * Test get_options defaults.
+	 *
+	 * @dataProvider get_test_get_options_defaults_data
+	 * @covers AMP_Options_Manager::get_options()
+	 * @covers AMP_Options_Manager::get_option()
+	 *
+	 * @param array|null $args           Theme support args.
+	 * @param string     $expected_mode  Expected mode.
+	 * @param array      $initial_option Initial option in DB.
+	 */
+	public function test_get_options_theme_support_defaults( $args, $expected_mode, $initial_option = [] ) {
+		update_option( AMP_Options_Manager::OPTION_NAME, $initial_option );
+		if ( isset( $args ) ) {
+			add_theme_support( 'amp', $args );
+		}
+		$this->assertEquals( $expected_mode, AMP_Options_Manager::get_option( 'theme_support' ) );
+	}
+
 	/**
 	 * Test check_supported_post_type_update_errors.
 	 *