diff --git a/wp-includes/class-wp-customize-setting.php b/wp-includes/class-wp-customize-setting.php
index a16b100795..7f1f98ac3b 100644
--- a/wp-includes/class-wp-customize-setting.php
+++ b/wp-includes/class-wp-customize-setting.php
@@ -696,6 +696,15 @@ class WP_Customize_Setting {
 		$is_core_type = ( 'option' === $this->type || 'theme_mod' === $this->type );
 
 		if ( ! $is_core_type && ! $this->is_multidimensional_aggregated ) {
+
+			// Use post value if previewed and a post value is present.
+			if ( $this->is_previewed ) {
+				$value = $this->post_value( null );
+				if ( null !== $value ) {
+					return $value;
+				}
+			}
+
 			$value = $this->get_root_value( $this->default );
 
 			/**
diff --git a/wp-includes/customize/class-wp-customize-custom-css-setting.php b/wp-includes/customize/class-wp-customize-custom-css-setting.php
index eb9379e425..eadd47c581 100644
--- a/wp-includes/customize/class-wp-customize-custom-css-setting.php
+++ b/wp-includes/customize/class-wp-customize-custom-css-setting.php
@@ -132,10 +132,13 @@ final class WP_Customize_Custom_CSS_Setting extends WP_Customize_Setting {
 	 * @return string
 	 */
 	public function value() {
-		$id_base = $this->id_data['base'];
-		if ( $this->is_previewed && null !== $this->post_value( null ) ) {
-			return $this->post_value();
+		if ( $this->is_previewed ) {
+			$post_value = $this->post_value( null );
+			if ( null !== $post_value ) {
+				return $post_value;
+			}
 		}
+		$id_base = $this->id_data['base'];
 		$value = '';
 		$post = wp_get_custom_css_post( $this->stylesheet );
 		if ( $post ) {
diff --git a/wp-includes/version.php b/wp-includes/version.php
index 0950d9f6ee..9ce114eecf 100644
--- a/wp-includes/version.php
+++ b/wp-includes/version.php
@@ -4,7 +4,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '4.7-beta4-39317';
+$wp_version = '4.7-beta4-39318';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.