diff --git a/src/wp-includes/customize/class-wp-customize-custom-css-setting.php b/src/wp-includes/customize/class-wp-customize-custom-css-setting.php
index 034e081484..ba4a58cf01 100644
--- a/src/wp-includes/customize/class-wp-customize-custom-css-setting.php
+++ b/src/wp-includes/customize/class-wp-customize-custom-css-setting.php
@@ -236,20 +236,9 @@ final class WP_Customize_Custom_CSS_Setting extends WP_Customize_Setting {
 		);
 
 		// Update post if it already exists, otherwise create a new one.
-		$post_id = null;
-		$query = new WP_Query( array(
-			'post_type' => 'custom_css',
-			'post_status' => get_post_stati(),
-			'name' => sanitize_title( $this->stylesheet ),
-			'number' => 1,
-			'no_found_rows' => true,
-			'cache_results' => true,
-			'update_post_meta_cache' => false,
-			'update_term_meta_cache' => false,
-			'suppress_filters' => true,
-		) );
-		if ( ! empty( $query->post ) ) {
-			$args['ID'] = $query->post->ID;
+		$post = wp_get_custom_css_post( $this->stylesheet );
+		if ( $post ) {
+			$args['ID'] = $post->ID;
 			$post_id = wp_update_post( wp_slash( $args ) );
 		} else {
 			$post_id = wp_insert_post( wp_slash( $args ) );
diff --git a/src/wp-includes/theme.php b/src/wp-includes/theme.php
index 646b2e4553..baad12f52d 100644
--- a/src/wp-includes/theme.php
+++ b/src/wp-includes/theme.php
@@ -1574,32 +1574,26 @@ function wp_custom_css_cb() {
 }
 
 /**
- * Fetch the saved Custom CSS content.
- *
- * Gets the content of a Custom CSS post that matches the
- * current theme.
+ * Fetch the `custom_css` post for a given theme.
  *
  * @since 4.7.0
  * @access public
  *
  * @param string $stylesheet Optional. A theme object stylesheet name. Defaults to the current theme.
- *
- * @return string The Custom CSS Post content.
+ * @return WP_Post|null The custom_css post or null if none exists.
  */
-function wp_get_custom_css( $stylesheet = '' ) {
-	$css = '';
-
+function wp_get_custom_css_post( $stylesheet = '' ) {
 	if ( empty( $stylesheet ) ) {
 		$stylesheet = get_stylesheet();
 	}
 
 	$custom_css_query_vars = array(
-		'post_type' => 'custom_css',
-		'post_status' => get_post_stati(),
-		'name' => sanitize_title( $stylesheet ),
-		'number' => 1,
-		'no_found_rows' => true,
-		'cache_results' => true,
+		'post_type'              => 'custom_css',
+		'post_status'            => get_post_stati(),
+		'name'                   => sanitize_title( $stylesheet ),
+		'number'                 => 1,
+		'no_found_rows'          => true,
+		'cache_results'          => true,
 		'update_post_meta_cache' => false,
 		'update_term_meta_cache' => false,
 	);
@@ -1607,10 +1601,9 @@ function wp_get_custom_css( $stylesheet = '' ) {
 	$post = null;
 	if ( get_stylesheet() === $stylesheet ) {
 		$post_id = get_theme_mod( 'custom_css_post_id' );
-		if ( ! $post_id ) {
+		if ( ! $post_id || ! get_post( $post_id ) ) {
 			$query = new WP_Query( $custom_css_query_vars );
 			$post = $query->post;
-
 			/*
 			 * Cache the lookup. See WP_Customize_Custom_CSS_Setting::update().
 			 * @todo This should get cleared if a custom_css post is added/removed.
@@ -1624,6 +1617,26 @@ function wp_get_custom_css( $stylesheet = '' ) {
 		$post = $query->post;
 	}
 
+	return $post;
+}
+
+/**
+ * Fetch the saved Custom CSS content.
+ *
+ * @since 4.7.0
+ * @access public
+ *
+ * @param string $stylesheet Optional. A theme object stylesheet name. Defaults to the current theme.
+ * @return string The Custom CSS Post content.
+ */
+function wp_get_custom_css( $stylesheet = '' ) {
+	$css = '';
+
+	if ( empty( $stylesheet ) ) {
+		$stylesheet = get_stylesheet();
+	}
+
+	$post = wp_get_custom_css_post( $stylesheet );
 	if ( $post ) {
 		$css = $post->post_content;
 	}
diff --git a/tests/phpunit/tests/customize/custom-css-setting.php b/tests/phpunit/tests/customize/custom-css-setting.php
index fea097644d..63c7c814c2 100644
--- a/tests/phpunit/tests/customize/custom-css-setting.php
+++ b/tests/phpunit/tests/customize/custom-css-setting.php
@@ -45,7 +45,7 @@ class Test_WP_Customize_Custom_CSS_Setting extends WP_UnitTestCase {
 		$wp_customize = $this->wp_customize;
 
 		do_action( 'customize_register', $this->wp_customize );
-		$this->setting = new WP_Customize_Custom_CSS_Setting( $this->wp_customize, 'custom_css[twentysixteen]' );
+		$this->setting = new WP_Customize_Custom_CSS_Setting( $this->wp_customize, 'custom_css[' . get_stylesheet() . ']' );
 		$this->wp_customize->add_setting( $this->setting );
 	}
 
@@ -78,7 +78,7 @@ class Test_WP_Customize_Custom_CSS_Setting extends WP_UnitTestCase {
 	function test_construct() {
 		$this->assertTrue( post_type_exists( 'custom_css' ) );
 		$this->assertEquals( 'custom_css', $this->setting->type );
-		$this->assertEquals( 'twentysixteen', $this->setting->stylesheet );
+		$this->assertEquals( get_stylesheet(), $this->setting->stylesheet );
 		$this->assertEquals( 'edit_css', $this->setting->capability );
 
 		$exception = null;
@@ -113,17 +113,36 @@ class Test_WP_Customize_Custom_CSS_Setting extends WP_UnitTestCase {
 		$this->setting->default = '/* Hello World */';
 		$this->assertEquals( $this->setting->default, $this->setting->value() );
 
+		$this->assertNull( wp_get_custom_css_post() );
+		$this->assertNull( wp_get_custom_css_post( $this->setting->stylesheet ) );
+		$this->assertNull( wp_get_custom_css_post( 'twentyten' ) );
+
 		$original_css = 'body { color: black; }';
-		$this->factory()->post->create( array(
+		$post_id = $this->factory()->post->create( array(
 			'post_title' => $this->setting->stylesheet,
 			'post_name' => $this->setting->stylesheet,
-			'post_content' => 'body { color: black; }',
+			'post_content' => $original_css,
 			'post_status' => 'publish',
 			'post_type' => 'custom_css',
 		) );
+		$twentyten_css = 'body { color: red; }';
+		$twentyten_post_id = $this->factory()->post->create( array(
+			'post_title' => 'twentyten',
+			'post_name' => 'twentyten',
+			'post_content' => $twentyten_css,
+			'post_status' => 'publish',
+			'post_type' => 'custom_css',
+		) );
+		$twentyten_setting = new WP_Customize_Custom_CSS_Setting( $this->wp_customize, 'custom_css[twentyten]' );
+
+		$this->assertEquals( $post_id, wp_get_custom_css_post()->ID );
+		$this->assertEquals( $post_id, wp_get_custom_css_post( $this->setting->stylesheet )->ID );
+		$this->assertEquals( $twentyten_post_id, wp_get_custom_css_post( 'twentyten' )->ID );
 
 		$this->assertEquals( $original_css, wp_get_custom_css( $this->setting->stylesheet ) );
 		$this->assertEquals( $original_css, $this->setting->value() );
+		$this->assertEquals( $twentyten_css, wp_get_custom_css( 'twentyten' ) );
+		$this->assertEquals( $twentyten_css, $twentyten_setting->value() );
 
 		$updated_css = 'body { color: blue; }';
 		$this->wp_customize->set_post_value( $this->setting->id, $updated_css );
@@ -138,6 +157,14 @@ class Test_WP_Customize_Custom_CSS_Setting extends WP_UnitTestCase {
 		$this->setting->preview();
 		$this->assertEquals( $previewed_css, $this->setting->value() );
 		$this->assertEquals( $previewed_css, wp_get_custom_css( $this->setting->stylesheet ) );
+
+		wp_delete_post( $post_id );
+		$this->assertNull( wp_get_custom_css_post() );
+		$this->assertNull( wp_get_custom_css_post( get_stylesheet() ) );
+		$this->assertEquals( $previewed_css, wp_get_custom_css( get_stylesheet() ), 'Previewed value remains in spite of deleted post.' );
+		wp_delete_post( $twentyten_post_id );
+		$this->assertNull( wp_get_custom_css_post( 'twentyten' ) );
+		$this->assertEquals( '', wp_get_custom_css( 'twentyten' ) );
 	}
 
 	/**