diff --git a/src/wp-content/themes/twentyeleven/readme.txt b/src/wp-content/themes/twentyeleven/readme.txt
index 924c74598f..e126d08f6f 100644
--- a/src/wp-content/themes/twentyeleven/readme.txt
+++ b/src/wp-content/themes/twentyeleven/readme.txt
@@ -22,7 +22,7 @@ For more information about Twenty Eleven please go to https://codex.wordpress.or
 
 == Copyright ==
 
-Twenty Eleven WordPress Theme, Copyright 2011-2018 WordPress.org & Automattic.com
+Twenty Eleven WordPress Theme, Copyright 2011-2019 WordPress.org & Automattic.com
 Twenty Eleven is Distributed under the terms of the GNU GPL
 
 This program is free software: you can redistribute it and/or modify
diff --git a/src/wp-content/themes/twentyfifteen/readme.txt b/src/wp-content/themes/twentyfifteen/readme.txt
index cb3d3555db..0e6a8af980 100644
--- a/src/wp-content/themes/twentyfifteen/readme.txt
+++ b/src/wp-content/themes/twentyfifteen/readme.txt
@@ -30,7 +30,7 @@ For more information about Twenty Fifteen please go to https://wordpress.org/sup
 
 == Copyright ==
 
-Twenty Fifteen WordPress Theme, Copyright 2014-2018 WordPress.org & Automattic.com
+Twenty Fifteen WordPress Theme, Copyright 2014-2019 WordPress.org & Automattic.com
 Twenty Fifteen is distributed under the terms of the GNU GPL
 
 This program is free software: you can redistribute it and/or modify
diff --git a/src/wp-content/themes/twentyfourteen/readme.txt b/src/wp-content/themes/twentyfourteen/readme.txt
index 3bbf5a34be..6a532e425a 100644
--- a/src/wp-content/themes/twentyfourteen/readme.txt
+++ b/src/wp-content/themes/twentyfourteen/readme.txt
@@ -22,7 +22,7 @@ For more information about Twenty Fourteen please go to https://codex.wordpress.
 
 == Copyright ==
 
-Twenty Fourteen WordPress Theme, Copyright 2013-2018 WordPress.org & Automattic.com
+Twenty Fourteen WordPress Theme, Copyright 2013-2019 WordPress.org & Automattic.com
 Twenty Fourteen is Distributed under the terms of the GNU GPL
 
 This program is free software: you can redistribute it and/or modify
diff --git a/src/wp-content/themes/twentynineteen/readme.txt b/src/wp-content/themes/twentynineteen/readme.txt
index 7436213081..08437d20dc 100644
--- a/src/wp-content/themes/twentynineteen/readme.txt
+++ b/src/wp-content/themes/twentynineteen/readme.txt
@@ -24,7 +24,7 @@ For more information about Twenty Nineteen please go to https://wordpress.org/su
 
 == Copyright ==
 
-Twenty Nineteen WordPress Theme, Copyright 2018 WordPress.org
+Twenty Nineteen WordPress Theme, Copyright 2018-2019 WordPress.org
 Twenty Nineteen is distributed under the terms of the GNU GPL
 
 This program is free software: you can redistribute it and/or modify
@@ -66,4 +66,4 @@ Initial release
 
 == Resources ==
 * normalize.css, © 2012-2018 Nicolas Gallagher and Jonathan Neal, MIT
-* Underscores, © 2012-2018 Automattic, Inc., GNU GPL v2 or later
+* Underscores, © 2012-2019 Automattic, Inc., GNU GPL v2 or later
diff --git a/src/wp-content/themes/twentynineteen/style-rtl.css b/src/wp-content/themes/twentynineteen/style-rtl.css
index 2e1f701bbc..84f857a608 100644
--- a/src/wp-content/themes/twentynineteen/style-rtl.css
+++ b/src/wp-content/themes/twentynineteen/style-rtl.css
@@ -16,7 +16,7 @@ Tags: one-column, flexible-header, accessibility-ready, custom-colors, custom-me
 This theme, like WordPress, is licensed under the GPL.
 Use it to make something cool, have fun, and share what you've learned with others.
 
-Twenty Nineteen is based on Underscores https://underscores.me/, (C) 2012-2018 Automattic, Inc.
+Twenty Nineteen is based on Underscores https://underscores.me/, (C) 2012-2019 Automattic, Inc.
 Underscores is distributed under the terms of the GNU GPL v2 or later.
 
 Normalizing styles have been helped along thanks to the fine work of
diff --git a/src/wp-content/themes/twentynineteen/style.css b/src/wp-content/themes/twentynineteen/style.css
index 075f41819e..c7122e0160 100644
--- a/src/wp-content/themes/twentynineteen/style.css
+++ b/src/wp-content/themes/twentynineteen/style.css
@@ -15,7 +15,7 @@ Tags: one-column, flexible-header, accessibility-ready, custom-colors, custom-me
 This theme, like WordPress, is licensed under the GPL.
 Use it to make something cool, have fun, and share what you've learned with others.
 
-Twenty Nineteen is based on Underscores https://underscores.me/, (C) 2012-2018 Automattic, Inc.
+Twenty Nineteen is based on Underscores https://underscores.me/, (C) 2012-2019 Automattic, Inc.
 Underscores is distributed under the terms of the GNU GPL v2 or later.
 
 Normalizing styles have been helped along thanks to the fine work of
diff --git a/src/wp-content/themes/twentynineteen/style.scss b/src/wp-content/themes/twentynineteen/style.scss
index 666c8dab3c..7807837289 100644
--- a/src/wp-content/themes/twentynineteen/style.scss
+++ b/src/wp-content/themes/twentynineteen/style.scss
@@ -14,7 +14,7 @@ Tags: one-column, flexible-header, accessibility-ready, custom-colors, custom-me
 This theme, like WordPress, is licensed under the GPL.
 Use it to make something cool, have fun, and share what you've learned with others.
 
-Twenty Nineteen is based on Underscores https://underscores.me/, (C) 2012-2018 Automattic, Inc.
+Twenty Nineteen is based on Underscores https://underscores.me/, (C) 2012-2019 Automattic, Inc.
 Underscores is distributed under the terms of the GNU GPL v2 or later.
 
 Normalizing styles have been helped along thanks to the fine work of
diff --git a/src/wp-content/themes/twentyseventeen/README.txt b/src/wp-content/themes/twentyseventeen/readme.txt
similarity index 98%
rename from src/wp-content/themes/twentyseventeen/README.txt
rename to src/wp-content/themes/twentyseventeen/readme.txt
index 5a67d3a7c2..bd41e2bdba 100644
--- a/src/wp-content/themes/twentyseventeen/README.txt
+++ b/src/wp-content/themes/twentyseventeen/readme.txt
@@ -22,7 +22,7 @@ For more information about Twenty Seventeen please go to https://wordpress.org/s
 
 == Copyright ==
 
-Twenty Seventeen WordPress Theme, Copyright 2016 WordPress.org
+Twenty Seventeen WordPress Theme, Copyright 2016-2019 WordPress.org
 Twenty Seventeen is distributed under the terms of the GNU GPL
 
 This program is free software: you can redistribute it and/or modify
diff --git a/src/wp-content/themes/twentysixteen/readme.txt b/src/wp-content/themes/twentysixteen/readme.txt
index 6ac5b6f674..e562dae7d2 100644
--- a/src/wp-content/themes/twentysixteen/readme.txt
+++ b/src/wp-content/themes/twentysixteen/readme.txt
@@ -28,7 +28,7 @@ For more information about Twenty Sixteen please go to https://wordpress.org/sup
 
 == Copyright ==
 
-Twenty Sixteen WordPress Theme, Copyright 2014-2018 WordPress.org
+Twenty Sixteen WordPress Theme, Copyright 2014-2019 WordPress.org
 Twenty Sixteen is distributed under the terms of the GNU GPL
 
 This program is free software: you can redistribute it and/or modify
diff --git a/src/wp-content/themes/twentyten/readme.txt b/src/wp-content/themes/twentyten/readme.txt
index ed6e25680b..de843ad754 100644
--- a/src/wp-content/themes/twentyten/readme.txt
+++ b/src/wp-content/themes/twentyten/readme.txt
@@ -21,7 +21,7 @@ For more information about Twenty Ten theme please go to https://codex.wordpress
 
 == Copyright ==
 
-Twenty Ten WordPress Theme, Copyright 2010-2018 WordPress.org & Automattic.com
+Twenty Ten WordPress Theme, Copyright 2010-2019 WordPress.org & Automattic.com
 Twenty Ten is Distributed under the terms of the GNU GPL
 
 This program is free software: you can redistribute it and/or modify
diff --git a/src/wp-content/themes/twentythirteen/readme.txt b/src/wp-content/themes/twentythirteen/readme.txt
index 492b5a1c24..a0d50ce35c 100644
--- a/src/wp-content/themes/twentythirteen/readme.txt
+++ b/src/wp-content/themes/twentythirteen/readme.txt
@@ -21,7 +21,7 @@ For more information about Twenty Thirteen please go to https://codex.wordpress.
 
 == Copyright ==
 
-Twenty Thirteen WordPress Theme, Copyright 2013-2018 WordPress.org & Automattic.com
+Twenty Thirteen WordPress Theme, Copyright 2013-2019 WordPress.org & Automattic.com
 Twenty Thirteen is Distributed under the terms of the GNU GPL
 
 This program is free software: you can redistribute it and/or modify
diff --git a/tests/phpunit/tests/theme.php b/tests/phpunit/tests/theme.php
index 2f114d43e2..c20906a121 100644
--- a/tests/phpunit/tests/theme.php
+++ b/tests/phpunit/tests/theme.php
@@ -210,6 +210,33 @@ class Tests_Theme extends WP_UnitTestCase {
 		}
 	}
 
+	/**
+	 * @ticket 48566
+	 */
+	function test_year_in_readme() {
+		// This test is designed to only run on trunk/master.
+		$this->skipOnAutomatedBranches();
+
+		foreach ( $this->default_themes as $theme ) {
+			$wp_theme = wp_get_theme( $theme );
+
+			$path_to_readme_txt = $wp_theme->get_theme_root() . '/' . $wp_theme->get_stylesheet() . '/readme.txt';
+			$this->assertFileExists( $path_to_readme_txt );
+			$readme    = file_get_contents( $path_to_readme_txt );
+			$this_year = gmdate( 'Y' );
+
+			preg_match( '#Copyright (\d+) WordPress.org#', $readme, $matches );
+			if ( $matches ) {
+				$this->assertEquals( $this_year, trim( $matches[1] ), "Bundled themes readme.txt's year needs to be updated to $this_year." );
+			}
+
+			preg_match( '#Copyright 20\d\d-(\d+) WordPress.org#', $readme, $matches );
+			if ( $matches ) {
+				$this->assertEquals( $this_year, trim( $matches[1] ), "Bundled themes readme.txt's year needs to be updated to $this_year." );
+			}
+		}
+	}
+
 	/**
 	 * @ticket 20897
 	 * @expectedDeprecated get_theme_data