diff --git a/wp-admin/includes/upgrade.php b/wp-admin/includes/upgrade.php
index 24f4ab4de8..171f82c935 100644
--- a/wp-admin/includes/upgrade.php
+++ b/wp-admin/includes/upgrade.php
@@ -1277,16 +1277,36 @@ function upgrade_network() {
 			$start += 20;
 		}
 	}
+
 	// 3.0
 	if ( $wp_current_db_version < 13576 )
 		update_site_option( 'global_terms_enabled', '1' );
+
 	// 3.3
 	if ( $wp_current_db_version < 19390 )
 		update_site_option( 'initial_db_version', $wp_current_db_version );
+
 	if ( $wp_current_db_version < 19470 ) {
 		if ( false === get_site_option( 'active_sitewide_plugins' ) )
 			update_site_option( 'active_sitewide_plugins', array() );
 	}
+
+	// 3.4
+	if ( $wp_current_db_version < 20148 ) {
+		// 'allowedthemes' keys things by stylesheet. 'allowed_themes' keyed things by name.
+		$allowedthemes  = get_site_option( 'allowedthemes'  );
+		$allowed_themes = get_site_option( 'allowed_themes' );
+		if ( false === $allowedthemes && is_array( $allowed_themes ) && $allowed_themes ) {
+			$converted = array();
+			$themes = wp_get_themes();
+			foreach ( $themes as $stylesheet => $theme_data ) {
+				if ( isset( $allowed_themes[ $theme_data->get('Name') ] ) )
+					$converted[ $stylesheet ] = true;
+			}
+			update_site_option( 'allowedthemes', $converted );
+			delete_site_option( 'allowed_themes' );
+		}
+	}
 }
 
 // The functions we use to actually do stuff
diff --git a/wp-includes/class-wp-theme.php b/wp-includes/class-wp-theme.php
index f1b29ff527..a72421037f 100644
--- a/wp-includes/class-wp-theme.php
+++ b/wp-includes/class-wp-theme.php
@@ -1084,33 +1084,8 @@ final class WP_Theme implements ArrayAccess {
 	 */
 	public static function get_allowed_on_network() {
 		static $allowed_themes;
-		if ( isset( $allowed_themes ) )
-			return $allowed_themes;
-
-		$allowed_themes = get_site_option( 'allowedthemes' );
-
-		// This is all super old MU back compat joy.
-		// 'allowedthemes' keys things by stylesheet. 'allowed_themes' keyed things by name.
-		if ( false === $allowed_themes ) {
-			$allowed_themes = get_site_option( 'allowed_themes' );
-			if ( ! is_array( $allowed_themes ) || empty( $allowed_themes ) ) {
-				$allowed_themes = array();
-			} else {
-				$converted = array();
-				$themes = wp_get_themes();
-				foreach ( $themes as $stylesheet => $theme_data ) {
-					if ( isset( $allowed_themes[ $theme_data->get('Name') ] ) )
-						$converted[ $stylesheet ] = true;
-				}
-				$allowed_themes = $converted;
-			}
-			// Set the option so we never have to go through this pain again.
-			if ( ( is_admin() && is_main_site() ) || is_network_admin() ) {
-				update_site_option( 'allowedthemes', $allowed_themes );
-				delete_site_option( 'allowed_themes' );
-			}
-		}
-
+		if ( ! isset( $allowed_themes ) )
+			$allowed_themes = (array) get_site_option( 'allowedthemes' );
 		return $allowed_themes;
 	}
 
@@ -1159,7 +1134,7 @@ final class WP_Theme implements ArrayAccess {
 				$allowed_themes[ $blog_id ] = $converted;
 			}
 			// Set the option so we never have to go through this pain again.
-			if ( is_admin() ) {
+			if ( is_admin() && $allowed_themes[ $blog_id ] ) {
 				if ( $current ) {
 					update_option( 'allowedthemes', $allowed_themes[ $blog_id ] );
 					delete_option( 'allowed_themes' );
diff --git a/wp-includes/version.php b/wp-includes/version.php
index b9bb765328..bae92df953 100644
--- a/wp-includes/version.php
+++ b/wp-includes/version.php
@@ -11,7 +11,7 @@ $wp_version = '3.4-alpha-20142';
  *
  * @global int $wp_db_version
  */
-$wp_db_version = 20080;
+$wp_db_version = 20148;
 
 /**
  * Holds the TinyMCE version