diff --git a/src/wp-includes/class-wp-customize-setting.php b/src/wp-includes/class-wp-customize-setting.php
index f5cb1bfcfc..fc78d07cb0 100644
--- a/src/wp-includes/class-wp-customize-setting.php
+++ b/src/wp-includes/class-wp-customize-setting.php
@@ -711,6 +711,11 @@ class WP_Customize_Setting {
 		} elseif ( $this->is_multidimensional_aggregated ) {
 			$root_value = self::$aggregated_multidimensionals[ $this->type ][ $id_base ]['root_value'];
 			$value = $this->multidimensional_get( $root_value, $this->id_data['keys'], $this->default );
+
+			// Ensure that the post value is used if the setting is previewed, since preview filters aren't applying on cached $root_value.
+			if ( $this->is_previewed ) {
+				$value = $this->post_value( $value );
+			}
 		} else {
 			$value = $this->get_root_value( $this->default );
 		}
diff --git a/tests/phpunit/tests/customize/setting.php b/tests/phpunit/tests/customize/setting.php
index 98990c53e0..94a3fe8a90 100644
--- a/tests/phpunit/tests/customize/setting.php
+++ b/tests/phpunit/tests/customize/setting.php
@@ -640,5 +640,29 @@ class Tests_WP_Customize_Setting extends WP_UnitTestCase {
 		}
 		return $validity;
 	}
+
+	/**
+	 * Ensure that WP_Customize_Setting::value() can return a previewed value for aggregated multidimensionals.
+	 *
+	 * @ticket 37294
+	 */
+	public function test_multidimensional_value_when_previewed() {
+		WP_Customize_Setting::reset_aggregated_multidimensionals();
+
+		$initial_value = 456;
+		set_theme_mod( 'nav_menu_locations', array(
+			'primary' => $initial_value,
+		) );
+		$setting_id = 'nav_menu_locations[primary]';
+
+		$setting = new WP_Customize_Setting( $this->manager, $setting_id );
+		$this->assertEquals( $initial_value, $setting->value() );
+
+		$override_value = -123456;
+		$this->manager->set_post_value( $setting_id, $override_value );
+		$setting->preview();
+
+		$this->assertEquals( $override_value, $setting->value() );
+	}
 }