diff --git a/wp-admin/admin.php b/wp-admin/admin.php
index d3e58d2549..184d5c2731 100644
--- a/wp-admin/admin.php
+++ b/wp-admin/admin.php
@@ -84,7 +84,7 @@ require_once(ABSPATH . 'wp-admin/includes/admin.php');
 auth_redirect();
 
 // Schedule trash collection
-if ( !wp_next_scheduled('wp_scheduled_delete') && !defined('WP_INSTALLING') )
+if ( ! wp_next_scheduled( 'wp_scheduled_delete' ) && ! wp_installing() )
 	wp_schedule_event(time(), 'daily', 'wp_scheduled_delete');
 
 set_screen_options();
diff --git a/wp-admin/includes/class-wp-upgrader.php b/wp-admin/includes/class-wp-upgrader.php
index 5b005ec30c..3ca66b8908 100644
--- a/wp-admin/includes/class-wp-upgrader.php
+++ b/wp-admin/includes/class-wp-upgrader.php
@@ -2604,7 +2604,7 @@ class WP_Automatic_Updater {
 		if ( defined( 'DISALLOW_FILE_MODS' ) && DISALLOW_FILE_MODS )
 			return true;
 
-		if ( defined( 'WP_INSTALLING' ) )
+		if ( wp_installing() )
 			return true;
 
 		// More fine grained control can be done through the WP_AUTO_UPDATE_CORE constant and filters.
diff --git a/wp-admin/includes/file.php b/wp-admin/includes/file.php
index a11bc95851..6fa47806db 100644
--- a/wp-admin/includes/file.php
+++ b/wp-admin/includes/file.php
@@ -1081,7 +1081,7 @@ function request_filesystem_credentials($form_post, $type = '', $error = false,
 			$stored_credentials['hostname'] .= ':' . $stored_credentials['port'];
 
 		unset($stored_credentials['password'], $stored_credentials['port'], $stored_credentials['private_key'], $stored_credentials['public_key']);
-		if ( ! defined( 'WP_INSTALLING' ) ) {
+		if ( ! wp_installing() ) {
 			update_option( 'ftp_credentials', $stored_credentials );
 		}
 		return $credentials;
diff --git a/wp-admin/includes/misc.php b/wp-admin/includes/misc.php
index e2cf976d28..776f04c968 100644
--- a/wp-admin/includes/misc.php
+++ b/wp-admin/includes/misc.php
@@ -261,7 +261,7 @@ function update_recently_edited( $file ) {
  * @param string $value
  */
 function update_home_siteurl( $old_value, $value ) {
-	if ( defined( "WP_INSTALLING" ) )
+	if ( wp_installing() )
 		return;
 
 	if ( is_multisite() && ms_is_switched() ) {
diff --git a/wp-admin/includes/translation-install.php b/wp-admin/includes/translation-install.php
index 8e1b827c47..2056838f00 100644
--- a/wp-admin/includes/translation-install.php
+++ b/wp-admin/includes/translation-install.php
@@ -94,7 +94,7 @@ function translations_api( $type, $args = null ) {
  *               in an error, an empty array will be returned.
  */
 function wp_get_available_translations() {
-	if ( ! defined( 'WP_INSTALLING' ) && false !== ( $translations = get_site_transient( 'available_translations' ) ) ) {
+	if ( ! wp_installing() && false !== ( $translations = get_site_transient( 'available_translations' ) ) ) {
 		return $translations;
 	}
 
diff --git a/wp-includes/functions.php b/wp-includes/functions.php
index a643d7ccb3..b6158ed261 100644
--- a/wp-includes/functions.php
+++ b/wp-includes/functions.php
@@ -1259,6 +1259,37 @@ function do_robots() {
 	echo apply_filters( 'robots_txt', $output, $public );
 }
 
+/**
+ * Check or set whether WordPress is in "installation" mode.
+ *
+ * If the `WP_INSTALLING` constant is defined during the bootstrap, `wp_installing()` will default to `true`.
+ *
+ * @since 4.4.0
+ *
+ * @staticvar bool $installing
+ *
+ * @param bool $is_installing Optional. True to set WP into Installing mode, false to turn Installing mode off.
+ *                            Omit this parameter if you only want to fetch the current status.
+ * @return bool True if WP is installing, otherwise false. When a `$is_installing` is passed, the function will
+ *              report whether WP was in installing mode prior to the change to `$is_installing`.
+ */
+function wp_installing( $is_installing = null ) {
+	static $installing = null;
+
+	// Support for the `WP_INSTALLING` constant, defined before WP is loaded.
+	if ( is_null( $installing ) ) {
+		$installing = defined( 'WP_INSTALLING' ) && WP_INSTALLING;
+	}
+
+	if ( ! is_null( $is_installing ) ) {
+		$old_installing = $installing;
+		$installing = $is_installing;
+		return (bool) $old_installing;
+	}
+
+	return (bool) $installing;
+}
+
 /**
  * Test whether blog is already installed.
  *
@@ -1285,7 +1316,7 @@ function is_blog_installed() {
 		return true;
 
 	$suppress = $wpdb->suppress_errors();
-	if ( ! defined( 'WP_INSTALLING' ) ) {
+	if ( ! wp_installing() ) {
 		$alloptions = wp_load_alloptions();
 	}
 	// If siteurl is not set to autoload, check it specifically
@@ -3337,7 +3368,7 @@ function dead_db() {
 	}
 
 	// If installing or in the admin, provide the verbose message.
-	if ( defined('WP_INSTALLING') || defined('WP_ADMIN') )
+	if ( wp_installing() || defined( 'WP_ADMIN' ) )
 		wp_die($wpdb->error);
 
 	// Otherwise, be terse.
diff --git a/wp-includes/l10n.php b/wp-includes/l10n.php
index b30fa417aa..2af07f17a0 100644
--- a/wp-includes/l10n.php
+++ b/wp-includes/l10n.php
@@ -53,7 +53,7 @@ function get_locale() {
 	// If multisite, check options.
 	if ( is_multisite() ) {
 		// Don't check blog option when installing.
-		if ( defined( 'WP_INSTALLING' ) || ( false === $ms_locale = get_option( 'WPLANG' ) ) ) {
+		if ( wp_installing() || ( false === $ms_locale = get_option( 'WPLANG' ) ) ) {
 			$ms_locale = get_network_option( 'WPLANG' );
 		}
 
@@ -635,7 +635,7 @@ function load_default_textdomain( $locale = null ) {
 		return $return;
 	}
 
-	if ( is_admin() || defined( 'WP_INSTALLING' ) || ( defined( 'WP_REPAIRING' ) && WP_REPAIRING ) ) {
+	if ( is_admin() || wp_installing() || ( defined( 'WP_REPAIRING' ) && WP_REPAIRING ) ) {
 		load_textdomain( 'default', WP_LANG_DIR . "/admin-$locale.mo" );
 	}
 
diff --git a/wp-includes/load.php b/wp-includes/load.php
index 560511a953..90db8290db 100644
--- a/wp-includes/load.php
+++ b/wp-includes/load.php
@@ -165,7 +165,7 @@ function wp_favicon_request() {
  * @global int $upgrading the unix timestamp marking when upgrading WordPress began.
  */
 function wp_maintenance() {
-	if ( !file_exists( ABSPATH . '.maintenance' ) || defined( 'WP_INSTALLING' ) )
+	if ( ! file_exists( ABSPATH . '.maintenance' ) || wp_installing() )
 		return;
 
 	global $upgrading;
@@ -475,12 +475,12 @@ function wp_start_object_cache() {
  */
 function wp_not_installed() {
 	if ( is_multisite() ) {
-		if ( ! is_blog_installed() && ! defined( 'WP_INSTALLING' ) ) {
+		if ( ! is_blog_installed() && ! wp_installing() ) {
 			nocache_headers();
 
 			wp_die( __( 'The site you have requested is not installed properly. Please contact the system administrator.' ) );
 		}
-	} elseif ( ! is_blog_installed() && ! defined( 'WP_INSTALLING' ) ) {
+	} elseif ( ! is_blog_installed() && ! wp_installing() ) {
 		nocache_headers();
 
 		require( ABSPATH . WPINC . '/kses.php' );
@@ -539,7 +539,7 @@ function wp_get_mu_plugins() {
 function wp_get_active_and_valid_plugins() {
 	$plugins = array();
 	$active_plugins = (array) get_option( 'active_plugins', array() );
-	if ( empty( $active_plugins ) || defined( 'WP_INSTALLING' ) )
+	if ( empty( $active_plugins ) || wp_installing() )
 		return $plugins;
 
 	$network_plugins = is_multisite() ? wp_get_active_network_plugins() : false;
diff --git a/wp-includes/ms-functions.php b/wp-includes/ms-functions.php
index 2aeda64fdf..ae5a242afa 100644
--- a/wp-includes/ms-functions.php
+++ b/wp-includes/ms-functions.php
@@ -1116,8 +1116,9 @@ function wpmu_create_blog( $domain, $path, $title, $user_id, $meta = array(), $s
 	if ( domain_exists($domain, $path, $site_id) )
 		return new WP_Error( 'blog_taken', __( 'Sorry, that site already exists!' ) );
 
-	if ( !defined('WP_INSTALLING') )
-		define( 'WP_INSTALLING', true );
+	if ( ! wp_installing() ) {
+		wp_installing( true );
+	}
 
 	if ( ! $blog_id = insert_blog($domain, $path, $site_id) )
 		return new WP_Error('insert_blog', __('Could not create site.'));
@@ -2172,7 +2173,7 @@ function wp_schedule_update_network_counts() {
 	if ( !is_main_site() )
 		return;
 
-	if ( !wp_next_scheduled('update_network_counts') && !defined('WP_INSTALLING') )
+	if ( ! wp_next_scheduled('update_network_counts') && ! wp_installing() )
 		wp_schedule_event(time(), 'twicedaily', 'update_network_counts');
 }
 
diff --git a/wp-includes/ms-settings.php b/wp-includes/ms-settings.php
index 861ee14abf..a490c22248 100644
--- a/wp-includes/ms-settings.php
+++ b/wp-includes/ms-settings.php
@@ -136,7 +136,7 @@ if ( !isset( $current_site ) || !isset( $current_blog ) ) {
 	}
 
 	// @todo Investigate when exactly this can occur.
-	if ( empty( $current_blog ) && defined( 'WP_INSTALLING' ) ) {
+	if ( empty( $current_blog ) && wp_installing() ) {
 		$current_blog = new stdClass;
 		$current_blog->blog_id = $blog_id = 1;
 	}
diff --git a/wp-includes/option.php b/wp-includes/option.php
index 2931c37fd1..701e485cf9 100644
--- a/wp-includes/option.php
+++ b/wp-includes/option.php
@@ -53,7 +53,7 @@ function get_option( $option, $default = false ) {
 	if ( defined( 'WP_SETUP_CONFIG' ) )
 		return false;
 
-	if ( ! defined( 'WP_INSTALLING' ) ) {
+	if ( ! wp_installing() ) {
 		// prevent non-existent options from triggering multiple queries
 		$notoptions = wp_cache_get( 'notoptions', 'options' );
 		if ( isset( $notoptions[ $option ] ) ) {
@@ -171,7 +171,7 @@ function form_option( $option ) {
 function wp_load_alloptions() {
 	global $wpdb;
 
-	if ( !defined( 'WP_INSTALLING' ) || !is_multisite() )
+	if ( ! wp_installing() || ! is_multisite() )
 		$alloptions = wp_cache_get( 'alloptions', 'options' );
 	else
 		$alloptions = false;
@@ -185,7 +185,7 @@ function wp_load_alloptions() {
 		foreach ( (array) $alloptions_db as $o ) {
 			$alloptions[$o->option_name] = $o->option_value;
 		}
-		if ( !defined( 'WP_INSTALLING' ) || !is_multisite() )
+		if ( ! wp_installing() || ! is_multisite() )
 			wp_cache_add( 'alloptions', $alloptions, 'options' );
 	}
 
@@ -204,7 +204,7 @@ function wp_load_alloptions() {
 function wp_load_core_site_options( $site_id = null ) {
 	global $wpdb;
 
-	if ( !is_multisite() || wp_using_ext_object_cache() || defined( 'WP_INSTALLING' ) )
+	if ( ! is_multisite() || wp_using_ext_object_cache() || wp_installing() )
 		return;
 
 	if ( empty($site_id) )
@@ -332,7 +332,7 @@ function update_option( $option, $value, $autoload = null ) {
 		wp_cache_set( 'notoptions', $notoptions, 'options' );
 	}
 
-	if ( ! defined( 'WP_INSTALLING' ) ) {
+	if ( ! wp_installing() ) {
 		$alloptions = wp_load_alloptions();
 		if ( isset( $alloptions[$option] ) ) {
 			$alloptions[ $option ] = $serialized_value;
@@ -433,7 +433,7 @@ function add_option( $option, $value = '', $deprecated = '', $autoload = 'yes' )
 	if ( ! $result )
 		return false;
 
-	if ( ! defined( 'WP_INSTALLING' ) ) {
+	if ( ! wp_installing() ) {
 		if ( 'yes' == $autoload ) {
 			$alloptions = wp_load_alloptions();
 			$alloptions[ $option ] = $serialized_value;
@@ -509,7 +509,7 @@ function delete_option( $option ) {
 	do_action( 'delete_option', $option );
 
 	$result = $wpdb->delete( $wpdb->options, array( 'option_name' => $option ) );
-	if ( ! defined( 'WP_INSTALLING' ) ) {
+	if ( ! wp_installing() ) {
 		if ( 'yes' == $row->autoload ) {
 			$alloptions = wp_load_alloptions();
 			if ( is_array( $alloptions ) && isset( $alloptions[$option] ) ) {
@@ -629,7 +629,7 @@ function get_transient( $transient ) {
 		$value = wp_cache_get( $transient, 'transient' );
 	} else {
 		$transient_option = '_transient_' . $transient;
-		if ( ! defined( 'WP_INSTALLING' ) ) {
+		if ( ! wp_installing() ) {
 			// If option is not in alloptions, it is not autoloaded and thus has a timeout
 			$alloptions = wp_load_alloptions();
 			if ( !isset( $alloptions[$transient_option] ) ) {
diff --git a/wp-includes/script-loader.php b/wp-includes/script-loader.php
index 1b28da52f1..a812ffe248 100644
--- a/wp-includes/script-loader.php
+++ b/wp-includes/script-loader.php
@@ -829,7 +829,7 @@ function wp_just_in_time_script_localization() {
 function wp_style_loader_src( $src, $handle ) {
 	global $_wp_admin_css_colors;
 
-	if ( defined('WP_INSTALLING') )
+	if ( wp_installing() )
 		return preg_replace( '#^wp-admin/#', './', $src );
 
 	if ( 'colors' == $handle ) {
diff --git a/wp-includes/theme.php b/wp-includes/theme.php
index 906da5176f..e1a0334ed9 100644
--- a/wp-includes/theme.php
+++ b/wp-includes/theme.php
@@ -771,7 +771,7 @@ function validate_current_theme() {
 	 *
 	 * @param bool true Validation flag to check the current theme.
 	 */
-	if ( defined('WP_INSTALLING') || ! apply_filters( 'validate_current_theme', true ) )
+	if ( wp_installing() || ! apply_filters( 'validate_current_theme', true ) )
 		return true;
 
 	if ( get_template() != WP_DEFAULT_THEME && !file_exists(get_template_directory() . '/index.php') ) {
diff --git a/wp-includes/update.php b/wp-includes/update.php
index c39322ee46..1def316be0 100644
--- a/wp-includes/update.php
+++ b/wp-includes/update.php
@@ -22,7 +22,7 @@
  * @param bool  $force_check Whether to bypass the transient cache and force a fresh update check. Defaults to false, true if $extra_stats is set.
  */
 function wp_version_check( $extra_stats = array(), $force_check = false ) {
-	if ( defined( 'WP_INSTALLING' ) ) {
+	if ( wp_installing() ) {
 		return;
 	}
 
@@ -187,7 +187,7 @@ function wp_version_check( $extra_stats = array(), $force_check = false ) {
  * @param array $extra_stats Extra statistics to report to the WordPress.org API.
  */
 function wp_update_plugins( $extra_stats = array() ) {
-	if ( defined( 'WP_INSTALLING' ) ) {
+	if ( wp_installing() ) {
 		return;
 	}
 
@@ -344,7 +344,7 @@ function wp_update_plugins( $extra_stats = array() ) {
  * @param array $extra_stats Extra statistics to report to the WordPress.org API.
  */
 function wp_update_themes( $extra_stats = array() ) {
-	if ( defined( 'WP_INSTALLING' ) ) {
+	if ( wp_installing() ) {
 		return;
 	}
 	global $wp_version;
@@ -636,16 +636,16 @@ function _maybe_update_themes() {
  * @since 3.1.0
  */
 function wp_schedule_update_checks() {
-	if ( !wp_next_scheduled('wp_version_check') && !defined('WP_INSTALLING') )
+	if ( ! wp_next_scheduled( 'wp_version_check' ) && ! wp_installing() )
 		wp_schedule_event(time(), 'twicedaily', 'wp_version_check');
 
-	if ( !wp_next_scheduled('wp_update_plugins') && !defined('WP_INSTALLING') )
+	if ( ! wp_next_scheduled( 'wp_update_plugins' ) && ! wp_installing() )
 		wp_schedule_event(time(), 'twicedaily', 'wp_update_plugins');
 
-	if ( !wp_next_scheduled('wp_update_themes') && !defined('WP_INSTALLING') )
+	if ( ! wp_next_scheduled( 'wp_update_themes' ) && ! wp_installing() )
 		wp_schedule_event(time(), 'twicedaily', 'wp_update_themes');
 
-	if ( ! wp_next_scheduled( 'wp_maybe_auto_update' ) && ! defined( 'WP_INSTALLING' ) ) {
+	if ( ! wp_next_scheduled( 'wp_maybe_auto_update' ) && ! wp_installing() ) {
 		// Schedule auto updates for 7 a.m. and 7 p.m. in the timezone of the site.
 		$next = strtotime( 'today 7am' );
 		$now = time();
diff --git a/wp-includes/version.php b/wp-includes/version.php
index bed17306dd..d47bfd3bcf 100644
--- a/wp-includes/version.php
+++ b/wp-includes/version.php
@@ -4,7 +4,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '4.4-alpha-34827';
+$wp_version = '4.4-alpha-34828';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.
diff --git a/wp-settings.php b/wp-settings.php
index 993a12096e..9a3afd840f 100644
--- a/wp-settings.php
+++ b/wp-settings.php
@@ -321,7 +321,7 @@ require_once( ABSPATH . WPINC . '/locale.php' );
 $GLOBALS['wp_locale'] = new WP_Locale();
 
 // Load the functions for the active theme, for both parent and child theme if applicable.
-if ( ! defined( 'WP_INSTALLING' ) || 'wp-activate.php' === $pagenow ) {
+if ( ! wp_installing() || 'wp-activate.php' === $pagenow ) {
 	if ( TEMPLATEPATH !== STYLESHEETPATH && file_exists( STYLESHEETPATH . '/functions.php' ) )
 		include( STYLESHEETPATH . '/functions.php' );
 	if ( file_exists( TEMPLATEPATH . '/functions.php' ) )