diff --git a/src/wp-includes/theme.php b/src/wp-includes/theme.php
index d643a9e289..8a675d44a9 100644
--- a/src/wp-includes/theme.php
+++ b/src/wp-includes/theme.php
@@ -187,7 +187,7 @@ function get_stylesheet_directory() {
  * @return string
  */
 function get_stylesheet_directory_uri() {
-	$stylesheet = get_stylesheet();
+	$stylesheet = str_replace( '%2F', '/', rawurlencode( get_stylesheet() ) );
 	$theme_root_uri = get_theme_root_uri( $stylesheet );
 	$stylesheet_dir_uri = "$theme_root_uri/$stylesheet";
 
@@ -318,7 +318,7 @@ function get_template_directory() {
  * @return string Template directory URI.
  */
 function get_template_directory_uri() {
-	$template = get_template();
+	$template = str_replace( '%2F', '/', rawurlencode( get_template() ) );
 	$theme_root_uri = get_theme_root_uri( $template );
 	$template_dir_uri = "$theme_root_uri/$template";
 
diff --git a/tests/phpunit/tests/theme/WPTheme.php b/tests/phpunit/tests/theme/WPTheme.php
index 44cedfcb02..4dbad859d4 100644
--- a/tests/phpunit/tests/theme/WPTheme.php
+++ b/tests/phpunit/tests/theme/WPTheme.php
@@ -110,4 +110,22 @@ class Tests_Theme_WPTheme extends WP_UnitTestCase {
 		$this->assertEquals( admin_url( 'customize.php?theme=theme+with+spaces' ), wp_customize_url( 'theme with spaces' ) );
 	}
 
+	/**
+	 * @ticket 21969
+	 */
+	function test_theme_uris_with_spaces() {
+		$callback = array( $this, 'filter_theme_with_spaces' );
+		add_filter( 'stylesheet', $callback );
+		add_filter( 'template', $callback );
+
+		$this->assertEquals( get_theme_root_uri() . '/subdir/theme%20with%20spaces', get_stylesheet_directory_uri() );
+		$this->assertEquals( get_theme_root_uri() . '/subdir/theme%20with%20spaces', get_template_directory_uri() );
+
+		remove_filter( 'stylesheet', $callback );
+		add_filter( 'template', $callback );
+	}
+
+	function filter_theme_with_spaces() {
+		return 'subdir/theme with spaces';
+	}
 }