diff --git src/wp-admin/load-scripts.php src/wp-admin/load-scripts.php
index 4c7d40e..e48b8ad 100644
--- src/wp-admin/load-scripts.php
+++ src/wp-admin/load-scripts.php
@@ -33,6 +33,15 @@ $out = '';
 $wp_scripts = new WP_Scripts();
 wp_default_scripts($wp_scripts);
 
+if ( isset( $_SERVER['HTTP_IF_NONE_MATCH'] ) && stripslashes( $_SERVER['HTTP_IF_NONE_MATCH'] ) === $wp_version && false === strpos( $wp_version, '-' ) ) {
+	$protocol = $_SERVER['SERVER_PROTOCOL'];
+	if ( ! in_array( $protocol, array( 'HTTP/1.1', 'HTTP/2', 'HTTP/2.0' ) ) ) {
+		$protocol = 'HTTP/1.0';
+	}
+	header( "$protocol 304 Not Modified" );
+	exit();
+}
+
 foreach ( $load as $handle ) {
 	if ( !array_key_exists($handle, $wp_scripts->registered) )
 		continue;
@@ -41,6 +50,7 @@ foreach ( $load as $handle ) {
 	$out .= get_file($path) . "\n";
 }
 
+header("Etag: $wp_version");
 header('Content-Type: application/javascript; charset=UTF-8');
 header('Expires: ' . gmdate( "D, d M Y H:i:s", time() + $expires_offset ) . ' GMT');
 header("Cache-Control: public, max-age=$expires_offset");
diff --git src/wp-admin/load-styles.php src/wp-admin/load-styles.php
index 2563e6f..f6771ca 100644
--- src/wp-admin/load-styles.php
+++ src/wp-admin/load-styles.php
@@ -30,6 +30,15 @@ $out = '';
 $wp_styles = new WP_Styles();
 wp_default_styles($wp_styles);
 
+if ( isset( $_SERVER['HTTP_IF_NONE_MATCH'] ) && stripslashes( $_SERVER['HTTP_IF_NONE_MATCH'] ) === $wp_version && false === strpos( $wp_version, '-' ) ) {
+	$protocol = $_SERVER['SERVER_PROTOCOL'];
+	if ( ! in_array( $protocol, array( 'HTTP/1.1', 'HTTP/2', 'HTTP/2.0' ) ) ) {
+		$protocol = 'HTTP/1.0';
+	}
+	header( "$protocol 304 Not Modified" );
+	exit();
+}
+
 foreach ( $load as $handle ) {
 	if ( !array_key_exists($handle, $wp_styles->registered) )
 		continue;
@@ -54,6 +63,7 @@ foreach ( $load as $handle ) {
 	}
 }
 
+header("Etag: $wp_version");
 header('Content-Type: text/css; charset=UTF-8');
 header('Expires: ' . gmdate( "D, d M Y H:i:s", time() + $expires_offset ) . ' GMT');
 header("Cache-Control: public, max-age=$expires_offset");