Index: src/wp-content/themes/twentyfifteen/functions.php
===================================================================
--- src/wp-content/themes/twentyfifteen/functions.php	(revision 29977)
+++ src/wp-content/themes/twentyfifteen/functions.php	(working copy)
@@ -330,3 +330,14 @@
  * @since Twenty Fifteen 1.0
  */
 require get_template_directory() . '/inc/customizer.php';
+
+/**
+ * Add Skype protocol to $allowed_protocols for the Social Links Menu.
+ *
+ * @since Twenty Fifteen 1.0
+ */
+function twentyfifteen_kses_allowed_protocols( $protocols ) {
+	$protocols[] = 'skype';
+	return $protocols;
+}
+add_filter( 'kses_allowed_protocols', 'twentyfifteen_kses_allowed_protocols' );
Index: src/wp-content/themes/twentyfifteen/style.css
===================================================================
--- src/wp-content/themes/twentyfifteen/style.css	(revision 29977)
+++ src/wp-content/themes/twentyfifteen/style.css	(working copy)
@@ -819,7 +819,7 @@
 }
 
 .social-navigation a[href*="skype.com"]:before,
-.social-navigation a[href*="skype:"]:before:before {
+.social-navigation a[href*="skype:"]:before {
 	content: "\f220";
 }