diff --git a/wp-includes/class-wp.php b/wp-includes/class-wp.php
index 8f66d98929..ce88c102cf 100644
--- a/wp-includes/class-wp.php
+++ b/wp-includes/class-wp.php
@@ -505,8 +505,8 @@ class WP {
 			}
 
 			$wp_last_modified .= ' GMT';
+			$wp_etag           = '"' . md5( $wp_last_modified ) . '"';
 
-			$wp_etag                  = '"' . md5( $wp_last_modified ) . '"';
 			$headers['Last-Modified'] = $wp_last_modified;
 			$headers['ETag']          = $wp_etag;
 
@@ -514,19 +514,24 @@ class WP {
 			if ( isset( $_SERVER['HTTP_IF_NONE_MATCH'] ) ) {
 				$client_etag = wp_unslash( $_SERVER['HTTP_IF_NONE_MATCH'] );
 			} else {
-				$client_etag = false;
+				$client_etag = '';
+			}
+
+			if ( isset( $_SERVER['HTTP_IF_MODIFIED_SINCE'] ) ) {
+				$client_last_modified = trim( $_SERVER['HTTP_IF_MODIFIED_SINCE'] );
+			} else {
+				$client_last_modified = '';
 			}
 
-			$client_last_modified = empty( $_SERVER['HTTP_IF_MODIFIED_SINCE'] ) ? '' : trim( $_SERVER['HTTP_IF_MODIFIED_SINCE'] );
 			// If string is empty, return 0. If not, attempt to parse into a timestamp.
 			$client_modified_timestamp = $client_last_modified ? strtotime( $client_last_modified ) : 0;
 
-			// Make a timestamp for our most recent modification..
+			// Make a timestamp for our most recent modification.
 			$wp_modified_timestamp = strtotime( $wp_last_modified );
 
-			if ( ( $client_last_modified && $client_etag ) ?
-					( ( $client_modified_timestamp >= $wp_modified_timestamp ) && ( $client_etag === $wp_etag ) ) :
-					( ( $client_modified_timestamp >= $wp_modified_timestamp ) || ( $client_etag === $wp_etag ) )
+			if ( ( $client_last_modified && $client_etag )
+				? ( ( $client_modified_timestamp >= $wp_modified_timestamp ) && ( $client_etag === $wp_etag ) )
+				: ( ( $client_modified_timestamp >= $wp_modified_timestamp ) || ( $client_etag === $wp_etag ) )
 			) {
 				$status        = 304;
 				$exit_required = true;
diff --git a/wp-includes/ms-files.php b/wp-includes/ms-files.php
index 6026a71db6..c909a32407 100644
--- a/wp-includes/ms-files.php
+++ b/wp-includes/ms-files.php
@@ -54,30 +54,36 @@ if ( WPMU_ACCEL_REDIRECT ) {
 	exit;
 }
 
-$last_modified = gmdate( 'D, d M Y H:i:s', filemtime( $file ) );
-$etag          = '"' . md5( $last_modified ) . '"';
-header( "Last-Modified: $last_modified GMT" );
-header( 'ETag: ' . $etag );
+$wp_last_modified = gmdate( 'D, d M Y H:i:s', filemtime( $file ) );
+$wp_etag          = '"' . md5( $wp_last_modified ) . '"';
+
+header( "Last-Modified: $wp_last_modified GMT" );
+header( 'ETag: ' . $wp_etag );
 header( 'Expires: ' . gmdate( 'D, d M Y H:i:s', time() + 100000000 ) . ' GMT' );
 
 // Support for conditional GET - use stripslashes() to avoid formatting.php dependency.
-$client_etag = isset( $_SERVER['HTTP_IF_NONE_MATCH'] ) ? stripslashes( $_SERVER['HTTP_IF_NONE_MATCH'] ) : false;
-
-if ( ! isset( $_SERVER['HTTP_IF_MODIFIED_SINCE'] ) ) {
-	$_SERVER['HTTP_IF_MODIFIED_SINCE'] = false;
+if ( isset( $_SERVER['HTTP_IF_NONE_MATCH'] ) ) {
+	$client_etag = stripslashes( $_SERVER['HTTP_IF_NONE_MATCH'] );
+} else {
+	$client_etag = '';
+}
+
+if ( isset( $_SERVER['HTTP_IF_MODIFIED_SINCE'] ) ) {
+	$client_last_modified = trim( $_SERVER['HTTP_IF_MODIFIED_SINCE'] );
+} else {
+	$client_last_modified = '';
 }
 
-$client_last_modified = trim( $_SERVER['HTTP_IF_MODIFIED_SINCE'] );
 // If string is empty, return 0. If not, attempt to parse into a timestamp.
 $client_modified_timestamp = $client_last_modified ? strtotime( $client_last_modified ) : 0;
 
-// Make a timestamp for our most recent modification...
-$modified_timestamp = strtotime( $last_modified );
+// Make a timestamp for our most recent modification.
+$wp_modified_timestamp = strtotime( $wp_last_modified );
 
 if ( ( $client_last_modified && $client_etag )
-	? ( ( $client_modified_timestamp >= $modified_timestamp ) && ( $client_etag == $etag ) )
-	: ( ( $client_modified_timestamp >= $modified_timestamp ) || ( $client_etag == $etag ) )
-	) {
+	? ( ( $client_modified_timestamp >= $wp_modified_timestamp ) && ( $client_etag === $wp_etag ) )
+	: ( ( $client_modified_timestamp >= $wp_modified_timestamp ) || ( $client_etag === $wp_etag ) )
+) {
 	status_header( 304 );
 	exit;
 }
diff --git a/wp-includes/version.php b/wp-includes/version.php
index 625993eb23..edb84c6356 100644
--- a/wp-includes/version.php
+++ b/wp-includes/version.php
@@ -16,7 +16,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '6.4-alpha-56394';
+$wp_version = '6.4-alpha-56395';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.