diff --git a/README.md b/README.md
index bb05979..9499280 100644
--- a/README.md
+++ b/README.md
@@ -64,6 +64,9 @@ If you like to have this feature, please leave a feature request in GitHub or th
 1. Statify Blacklist settings page
 
 ## Changelog ##
+### 1.2.0 / (work in progress) ###
+* Switched from `in_array()` to faster `isset()` for referer checking
+
 ### 1.1.2 / 17.08.2016 ###
 * Prepared for localization
 
diff --git a/inc/statifyblacklist.class.php b/inc/statifyblacklist.class.php
index a590846..ad58dcb 100644
--- a/inc/statifyblacklist.class.php
+++ b/inc/statifyblacklist.class.php
@@ -100,6 +100,7 @@ class StatifyBlacklist {
 	 * @return  TRUE if referer matches blacklist.
 	 *
 	 * @since   1.0.0
+	 * @changed 1.2.0
 	 */
 	public static function apply_blacklist_filter() {
 		/* Skip if blacklist is inactive */
@@ -121,6 +122,6 @@ class StatifyBlacklist {
 
 		/* Check blacklist */
 
-		return in_array( $referer, $blacklist );
+		return isset( $blacklist[ $referer ] );
 	}
 }
diff --git a/inc/statifyblacklist_admin.class.php b/inc/statifyblacklist_admin.class.php
index f2ad789..375551b 100644
--- a/inc/statifyblacklist_admin.class.php
+++ b/inc/statifyblacklist_admin.class.php
@@ -18,7 +18,7 @@ class StatifyBlacklist_Admin extends StatifyBlacklist {
 	public static function update_options( $options ) {
 		if ( isset( $options ) && current_user_can( 'manage_options' ) ) {
 			/* Sanitize URLs and remove empty inputs */
-			$givenReferer = $options['referer'];
+			$givenReferer     = $options['referer'];
 			$sanitizedReferer = self::sanitizeURLs( $givenReferer );
 
 			/* Abort on errors */
@@ -109,7 +109,7 @@ class StatifyBlacklist_Admin extends StatifyBlacklist {
 	 * Filter database for cleanup.
 	 *
 	 * @since   1.1.0
-	 * @changed 1.1.1
+	 * @changed 1.2.1
 	 */
 	public static function cleanup_database() {
 		/* Check user permissions */
@@ -123,7 +123,7 @@ class StatifyBlacklist_Admin extends StatifyBlacklist {
 		$referer = self::sanitizeURLs( self::$_options['referer'] );
 
 		/* Build filter regexp */
-		$refererRegexp = str_replace( '.', '\.', implode( '|', $referer ) );
+		$refererRegexp = str_replace( '.', '\.', implode( '|', array_flip( $referer ) ) );
 		if ( ! empty( $refererRegexp ) ) {
 			/* Execute filter on database */
 			$wpdb->query(
@@ -144,15 +144,18 @@ class StatifyBlacklist_Admin extends StatifyBlacklist {
 	 * @return array  sanitized array
 	 *
 	 * @since    1.1.1
+	 * @changed  1.2.0
 	 */
 	private static function sanitizeURLs( $urls ) {
-		return array_filter(
-			array_map(
-				function ( $r ) {
-					return preg_replace( '/[^\da-z\.-]/i', '', filter_var( $r, FILTER_SANITIZE_URL ) );
-				},
-				$urls
+		return array_flip(
+			array_filter(
+				array_map(
+					function ( $r ) {
+						return preg_replace( '/[^\da-z\.-]/i', '', filter_var( $r, FILTER_SANITIZE_URL ) );
+					},
+					array_flip( $urls )
+				)
 			)
 		);
 	}
-}
\ No newline at end of file
+}
diff --git a/inc/statifyblacklist_system.class.php b/inc/statifyblacklist_system.class.php
index a8f6b43..2319aa9 100644
--- a/inc/statifyblacklist_system.class.php
+++ b/inc/statifyblacklist_system.class.php
@@ -28,7 +28,10 @@ class StatifyBlacklist_System extends StatifyBlacklist {
 				switch_to_blog( $site_id );
 				add_option(
 					'statify-blacklist',
-					array()
+					array(
+						'activate-referer' => 0,
+						'referer'          => array()
+					)
 				);
 			}
 
@@ -36,7 +39,10 @@ class StatifyBlacklist_System extends StatifyBlacklist {
 		} else {
 			add_option(
 				'statify-blacklist',
-				array()
+				array(
+					'activate-referer' => 0,
+					'referer'          => array()
+				)
 			);
 		}
 	}
@@ -66,4 +72,28 @@ class StatifyBlacklist_System extends StatifyBlacklist {
 
 		delete_option( 'statify-blacklist' );
 	}
-}
\ No newline at end of file
+
+
+	/**
+	 * Upgrade plugin options.
+	 *
+	 * @param object $upgrader Upgrader object (unused)
+	 * @param array $options Options array
+	 *
+	 * @since 1.2.0
+	 */
+	public static function upgrade() {
+		self::update_options();
+		/* Check if config array is not associative (pre 1.2.0) */
+		if ( array_keys( self::$_options['referer'] ) === range( 0, count( self::$_options['referer'] ) - 1 ) ) {
+			/* Flip referer array to make domains keys */
+			$options            = self::$_options;
+			$options['referer'] = array_flip( self::$_options['referer'] );
+			if ( ( is_multisite() && array_key_exists( STATIFYBLACKLIST_BASE, (array) get_site_option( 'active_sitewide_plugins' ) ) ) ) {
+				update_site_option( 'statify-blacklist', $options );
+			} else {
+				update_option( 'statify-blacklist', $options );
+			}
+		}
+	}
+}
diff --git a/statify-blacklist.php b/statify-blacklist.php
index 8f7dd54..99bfd50 100644
--- a/statify-blacklist.php
+++ b/statify-blacklist.php
@@ -8,7 +8,7 @@ Author:      Stefan Kalscheuer
 Author URI:  https://stklcode.de
 Plugin URI:  https://wordpress.org/plugins/statify-blacklist
 License:     GPLv3 or later
-Version:     1.1.2
+Version:     1.2.0
 */
 
 /* Quit */
@@ -26,6 +26,9 @@ register_activation_hook( STATIFYBLACKLIST_FILE, array( 'StatifyBlacklist_System
 
 register_uninstall_hook( STATIFYBLACKLIST_FILE, array( 'StatifyBlacklist_System', 'uninstall' ) );
 
+/* Upgrade hook to v1.2.0 */
+register_activation_hook( STATIFYBLACKLIST_FILE, array( 'StatifyBlacklist_System', 'upgrade' ) );
+
 /* Autoload */
 spl_autoload_register( 'statifyBlacklist_autoload' );
 
diff --git a/views/settings_page.php b/views/settings_page.php
old mode 100644
new mode 100755
index 7e0f5aa..d5ba191
--- a/views/settings_page.php
+++ b/views/settings_page.php
@@ -28,7 +28,7 @@ if ( ! empty( $_POST['statifyblacklist'] ) ) {
 		$statifyBlacklistUpdateResult = StatifyBlacklist_Admin::update_options(
 			array(
 				'active_referer' => (int) @$_POST['statifyblacklist']['active_referer'],
-				'referer'        => $referer
+				'referer'        => array_flip( $referer )
 			)
 		);
 
@@ -76,12 +76,11 @@ if ( ! empty( $_POST['statifyblacklist'] ) ) {
 					<?php esc_html_e( 'Referer blacklist:', 'statify-blacklist' ); ?><br/>
 					<textarea cols="40" rows="5" name="statifyblacklist[referer]" id="statify-blacklist_referer"><?php
 						if ( isset( $statifyBlacklistUpdateResult ) && $statifyBlacklistUpdateResult !== false ) {
-							print esc_html( implode( "\r\n", $statifyBlacklistUpdateResult ) );
+							print esc_html( implode( "\r\n", array_keys( $statifyBlacklistUpdateResult ) ) );
 						} else {
-							print esc_html( implode( "\r\n", StatifyBlacklist::$_options['referer'] ) );
+							print esc_html( implode( "\r\n", array_keys( StatifyBlacklist::$_options['referer'] ) ) );
 						}
-						?></textarea>
-					<br />
+						?></textarea><br/>
 					<small>
 						(<?php esc_html_e( 'Add one domain (without subdomains) each line, e.g. example.com', 'statify-blacklist' ); ?>
 						)
@@ -92,12 +91,12 @@ if ( ! empty( $_POST['statifyblacklist'] ) ) {
 		<?php wp_nonce_field( 'statify-blacklist-settings' ); ?>
 
 		<p class="submit">
-			<input class="button-primary" type="submit" name="submit" value="<?php _e( 'Save Changes' ) ?>" />
-		<hr />
+			<input class="button-primary" type="submit" name="submit" value="<?php _e( 'Save Changes' ) ?>">
+		<hr>
 		<input class="button-secondary" type="submit" name="cleanUp"
 		       value="<?php esc_html_e( 'CleanUp Database', 'statify-blacklist' ) ?>"
 		       onclick="return confirm('Do you really want to apply filters to database? This cannot be undone.');">
-		<br />
+		<br>
 		<small><?php esc_html_e( 'Applies filter (even if disabled) to data stored in database. This cannot be undone!', 'statify-blacklist' ); ?></small>
 		</p>
 	</form>