Index: wp-admin/customize.php
===================================================================
--- wp-admin/customize.php	(revision 25570)
+++ wp-admin/customize.php	(working copy)
@@ -80,9 +80,13 @@
 				submit_button( $save_text, 'primary save', 'save', false );
 			?>
 			<span class="spinner"></span>
-			<a class="back button" href="<?php echo esc_url( $return ? $return : admin_url( 'themes.php' ) ); ?>">
-				<?php _e( 'Cancel' ); ?>
-			</a>
+                        <?php
+                                $close_url = $return ? $return : admin_url( 'themes.php' );
+                                $close_url = apply_filters( 'customize_close_url', $close_url );
+                        ?>
+                        <a class="back button" href="<?php echo esc_url( $close_url ); ?>">
+                                <?php _e( 'Cancel' ); ?>
+                        </a>
 		</div>
 
 		<?php