Index: src/wp-content/themes/twentyfifteen/functions.php
===================================================================
--- src/wp-content/themes/twentyfifteen/functions.php	(revision 36742)
+++ src/wp-content/themes/twentyfifteen/functions.php	(working copy)
@@ -103,6 +103,14 @@
 		'aside', 'image', 'video', 'quote', 'link', 'gallery', 'status', 'audio', 'chat'
 	) );
 
+	/*
+	 * Enable support for custom logo.
+	 *
+	 * @since Twenty Fifteen 1.5
+	 */
+	add_image_size( 'twentyfifteen-logo', 248, 248 );
+	add_theme_support( 'custom-logo', array( 'size' => 'twentyfifteen-logo' ) );
+
 	$color_scheme  = twentyfifteen_get_color_scheme();
 	$default_color = trim( $color_scheme[0], '#' );
 
Index: src/wp-content/themes/twentyfifteen/header.php
===================================================================
--- src/wp-content/themes/twentyfifteen/header.php	(revision 36742)
+++ src/wp-content/themes/twentyfifteen/header.php	(working copy)
@@ -29,6 +29,8 @@
 		<header id="masthead" class="site-header" role="banner">
 			<div class="site-branding">
 				<?php
+					twentyfifteen_the_custom_logo();
+
 					if ( is_front_page() && is_home() ) : ?>
 						<h1 class="site-title"><a href="<?php echo esc_url( home_url( '/' ) ); ?>" rel="home"><?php bloginfo( 'name' ); ?></a></h1>
 					<?php else : ?>
Index: src/wp-content/themes/twentyfifteen/inc/template-tags.php
===================================================================
--- src/wp-content/themes/twentyfifteen/inc/template-tags.php	(revision 36742)
+++ src/wp-content/themes/twentyfifteen/inc/template-tags.php	(working copy)
@@ -241,3 +241,20 @@
 }
 add_filter( 'excerpt_more', 'twentyfifteen_excerpt_more' );
 endif;
+
+if ( ! function_exists( 'twentyfifteen_the_custom_logo' ) ) :
+/**
+ * Displays the optional custom logo.
+ *
+ * Returns early if the custom logo is not available.
+ *
+ * @since Twenty Fifteen 1.5
+ */
+function twentyfifteen_the_custom_logo() {
+	if ( ! function_exists( 'the_custom_logo' ) ) {
+		return;
+	} else {
+		the_custom_logo();
+	}
+}
+endif;
Index: src/wp-content/themes/twentyfifteen/style.css
===================================================================
--- src/wp-content/themes/twentyfifteen/style.css	(revision 36742)
+++ src/wp-content/themes/twentyfifteen/style.css	(working copy)
@@ -1312,6 +1312,15 @@
 	margin-bottom: 0;
 }
 
+.custom-logo {
+	max-height: 84px;
+	width: auto;
+}
+
+.wp-custom-logo .site-title {
+	margin-top: 0.545454545em;
+}
+
 .site-description {
 	display: none;
 	font-family: "Noto Sans", sans-serif;
@@ -3085,6 +3094,14 @@
 		line-height: 1.2069;
 	}
 
+	.custom-logo {
+		max-height: 105px;
+	}
+
+	.wp-custom-logo .site-title {
+		margin-top: 0.482758621em;
+	}
+
 	.site-description {
 		font-size: 14px;
 		font-size: 1.4rem;
@@ -3707,6 +3724,14 @@
 		line-height: 1.25;
 	}
 
+	.custom-logo {
+		max-height: 104px;
+	}
+
+	.wp-custom-logo .site-title {
+		margin-top: 0.5em;
+	}
+
 	.site-description {
 		font-size: 16px;
 		font-size: 1.6rem;
@@ -4342,6 +4367,14 @@
 		line-height: 1.3636;
 	}
 
+	.custom-logo {
+		max-height: none;
+	}
+
+	.wp-custom-logo .site-title {
+		margin-top: 0.545454545em;
+	}
+
 	.site-description {
 		font-size: 12px;
 		font-size: 1.2rem;
@@ -4961,6 +4994,10 @@
 		line-height: 1.1667;
 	}
 
+	.wp-custom-logo .site-title {
+		margin-top: 0.583333333em;
+	}
+
 	.site-description {
 		font-size: 14px;
 		font-size: 1.4rem;
@@ -5499,6 +5536,10 @@
 		line-height: 1.1852;
 	}
 
+	.wp-custom-logo .site-title {
+		margin-top: 0.592592593em;
+	}
+
 	.site-description {
 		font-size: 16px;
 		font-size: 1.6rem;