diff --git a/lib/AtomFeed.php b/lib/AtomFeed.php
index d8f457e8..28d2845f 100644
--- a/lib/AtomFeed.php
+++ b/lib/AtomFeed.php
@@ -55,7 +55,7 @@ class AtomFeed extends Feed{
 		$currentEntries = [];
 		foreach($this->Entries as $entry){
 			$obj = new StdClass();
-			if(is_a($entry, 'Ebook')){
+			if($entry instanceof Ebook){
 				$obj->Updated = $entry->Updated->format('Y-m-d\TH:i:s\Z');
 				$obj->Id = SITE_URL . $entry->Url;
 			}
diff --git a/lib/DbConnection.php b/lib/DbConnection.php
index 393dcb99..1c4fd68e 100644
--- a/lib/DbConnection.php
+++ b/lib/DbConnection.php
@@ -93,7 +93,7 @@ class DbConnection{
 		foreach($params as $parameter){
 			$name++;
 
-			if(is_a($parameter, 'DateTime') || is_a($parameter, 'DateTimeImmutable')){
+			if($parameter instanceof DateTimeInterface){
 				$parameter = $parameter->format('Y-m-d H:i:s');
 			}
 			elseif(is_bool($parameter)){
diff --git a/lib/OpdsFeed.php b/lib/OpdsFeed.php
index d30ab1b7..ffa9012d 100644
--- a/lib/OpdsFeed.php
+++ b/lib/OpdsFeed.php
@@ -27,7 +27,7 @@ class OpdsFeed extends AtomFeed{
 	protected function SaveUpdated(string $entryId, DateTime $updated): void{
 		// Only save the updated timestamp for the given entry ID in this file
 		foreach($this->Entries as $entry){
-			if(is_a($entry, 'OpdsNavigationEntry')){
+			if($entry instanceof OpdsNavigationEntry){
 				if($entry->Id == SITE_URL . $entryId){
 					$entry->Updated = $updated;
 				}
diff --git a/www/sessions/new.php b/www/sessions/new.php
index e3b826db..7096101f 100644
--- a/www/sessions/new.php
+++ b/www/sessions/new.php
@@ -17,7 +17,7 @@ $passwordRequired = false;
 http_response_code(401);
 
 if($exception){
-	if(is_a($exception, 'Exceptions\PasswordRequiredException')){
+	if($exception instanceof Exceptions\PasswordRequiredException){
 		// This login requires a password to proceed.
 		// Prompt the user for a password.
 		http_response_code(401);