diff --git a/src/wp-admin/network/themes.php b/src/wp-admin/network/themes.php
index 29dd9e5b57..9466c41017 100644
--- a/src/wp-admin/network/themes.php
+++ b/src/wp-admin/network/themes.php
@@ -287,7 +287,7 @@ if ( isset( $_GET['enabled'] ) ) {
 $wp_list_table->views();
 
 if ( 'broken' == $status )
-	echo '<p class="clear">' . __('The following themes are installed but incomplete. Themes must have a stylesheet and a template.') . '</p>';
+	echo '<p class="clear">' . __( 'The following themes are installed but incomplete.' ) . '</p>';
 ?>
 
 <form method="post">
diff --git a/src/wp-admin/themes.php b/src/wp-admin/themes.php
index d229d9261d..d964fc22aa 100644
--- a/src/wp-admin/themes.php
+++ b/src/wp-admin/themes.php
@@ -295,7 +295,7 @@ if ( ! is_multisite() && current_user_can('edit_themes') && $broken_themes = wp_
 
 <div class="broken-themes">
 <h3><?php _e('Broken Themes'); ?></h3>
-<p><?php _e('The following themes are installed but incomplete. Themes must have a stylesheet and a template.'); ?></p>
+<p><?php _e( 'The following themes are installed but incomplete.' ); ?></p>
 
 <?php
 $can_delete = current_user_can( 'delete_themes' );
diff --git a/src/wp-includes/class-wp-theme.php b/src/wp-includes/class-wp-theme.php
index bdd408435b..a765655363 100644
--- a/src/wp-includes/class-wp-theme.php
+++ b/src/wp-includes/class-wp-theme.php
@@ -268,7 +268,14 @@ final class WP_Theme implements ArrayAccess {
 		if ( ! $this->template && ! ( $this->template = $this->headers['Template'] ) ) {
 			$this->template = $this->stylesheet;
 			if ( ! file_exists( $this->theme_root . '/' . $this->stylesheet . '/index.php' ) ) {
-				$this->errors = new WP_Error( 'theme_no_index', __( 'Template is missing.' ) );
+				$error_message = sprintf(
+					/* translators: 1: index.php, 2: Codex URL, 3: style.css */
+					__( 'Template is missing. Standalone themes need to have a %1$s template file. <a href="%2$s">Child themes</a> need to have a Template header in the %3$s stylesheet.' ),
+					'<code>index.php</code>',
+					__( 'https://codex.wordpress.org/Child_Themes' ),
+					'<code>style.css</code>'
+				);
+				$this->errors = new WP_Error( 'theme_no_index', $error_message );
 				$this->cache_add( 'theme', array( 'headers' => $this->headers, 'errors' => $this->errors, 'stylesheet' => $this->stylesheet, 'template' => $this->template ) );
 				return;
 			}