diff --git a/bin/baseline.neon b/bin/baseline.neon
index ff9b193b..e98ddcf3 100644
--- a/bin/baseline.neon
+++ b/bin/baseline.neon
@@ -48,12 +48,6 @@ parameters:
 			count: 2
 			path: ../includes/acf-field-functions.php
 
-		-
-			message: '#^Constant ACF_PATH not found\.$#'
-			identifier: constant.notFound
-			count: 1
-			path: ../includes/acf-helper-functions.php
-
 		-
 			message: '#^Function acf_set_filters\(\) should return array but return statement is missing\.$#'
 			identifier: return.missing
@@ -126,24 +120,12 @@ parameters:
 			count: 1
 			path: ../includes/acf-user-functions.php
 
-		-
-			message: '#^Constant ACF_PATH not found\.$#'
-			identifier: constant.notFound
-			count: 1
-			path: ../includes/acf-utility-functions.php
-
 		-
 			message: '#^Action callback returns string but should not return anything\.$#'
 			identifier: return.void
 			count: 1
 			path: ../includes/admin/admin-internal-post-type-list.php
 
-		-
-			message: '#^Constant ACF_PATH not found\.$#'
-			identifier: constant.notFound
-			count: 1
-			path: ../includes/admin/admin-internal-post-type-list.php
-
 		-
 			message: '#^Action callback returns string but should not return anything\.$#'
 			identifier: return.void
@@ -168,12 +150,6 @@ parameters:
 			count: 2
 			path: ../includes/admin/admin-upgrade.php
 
-		-
-			message: '#^Constant ACF_UPGRADE_VERSION not found\.$#'
-			identifier: constant.notFound
-			count: 1
-			path: ../includes/admin/admin-upgrade.php
-
 		-
 			message: '#^Action callback returns string but should not return anything\.$#'
 			identifier: return.void
@@ -288,12 +264,6 @@ parameters:
 			count: 1
 			path: ../includes/admin/views/tools/tools.php
 
-		-
-			message: '#^Constant ACF_VERSION not found\.$#'
-			identifier: constant.notFound
-			count: 2
-			path: ../includes/admin/views/upgrade/network.php
-
 		-
 			message: '#^Variable \$button_text might not be defined\.$#'
 			identifier: variable.undefined
@@ -312,12 +282,6 @@ parameters:
 			count: 1
 			path: ../includes/admin/views/upgrade/notice.php
 
-		-
-			message: '#^Constant ACF_VERSION not found\.$#'
-			identifier: constant.notFound
-			count: 1
-			path: ../includes/admin/views/upgrade/upgrade.php
-
 		-
 			message: '#^Function remove_filter invoked with 4 parameters, 2\-3 required\.$#'
 			identifier: arguments.count
@@ -360,12 +324,6 @@ parameters:
 			count: 1
 			path: ../includes/api/api-term.php
 
-		-
-			message: '#^Constant ACF_VERSION not found\.$#'
-			identifier: constant.notFound
-			count: 3
-			path: ../includes/blocks.php
-
 		-
 			message: '#^Access to an undefined property ACF_Data\:\:\$site_aliases\.$#'
 			identifier: property.notFound
@@ -618,24 +576,6 @@ parameters:
 			count: 1
 			path: ../includes/revisions.php
 
-		-
-			message: '#^Constant ACF_VERSION not found\.$#'
-			identifier: constant.notFound
-			count: 1
-			path: ../includes/third-party.php
-
-		-
-			message: '#^Constant ACF_UPGRADE_VERSION not found\.$#'
-			identifier: constant.notFound
-			count: 2
-			path: ../includes/upgrades.php
-
-		-
-			message: '#^Constant ACF_VERSION not found\.$#'
-			identifier: constant.notFound
-			count: 3
-			path: ../includes/upgrades.php
-
 		-
 			message: '#^Access to an undefined property acf_validation\:\:\$errors\.$#'
 			identifier: property.notFound
@@ -648,36 +588,6 @@ parameters:
 			count: 1
 			path: ../includes/wpml.php
 
-		-
-			message: '#^Constant ACF_BASENAME not found\.$#'
-			identifier: constant.notFound
-			count: 2
-			path: ../secure-custom-fields.php
-
-		-
-			message: '#^Constant ACF_FIELD_API_VERSION not found\.$#'
-			identifier: constant.notFound
-			count: 3
-			path: ../secure-custom-fields.php
-
-		-
-			message: '#^Constant ACF_MAJOR_VERSION not found\.$#'
-			identifier: constant.notFound
-			count: 4
-			path: ../secure-custom-fields.php
-
-		-
-			message: '#^Constant ACF_PATH not found\.$#'
-			identifier: constant.notFound
-			count: 2
-			path: ../secure-custom-fields.php
-
-		-
-			message: '#^Constant ACF_VERSION not found\.$#'
-			identifier: constant.notFound
-			count: 2
-			path: ../secure-custom-fields.php
-
 		-
 			message: '#^One or more @param tags has an invalid name or invalid syntax\.$#'
 			identifier: phpDoc.parseError
diff --git a/bin/phpstan-bootstrap.php b/bin/phpstan-bootstrap.php
new file mode 100644
index 00000000..96201ebc
--- /dev/null
+++ b/bin/phpstan-bootstrap.php
@@ -0,0 +1,13 @@
+<?php
+/**
+ * Bootstrap the plugin for PHPStan.
+ *
+ * Loads the plugin file as the entry point for PHPStan.
+ *
+ * @package WordPress/Secure-Custom-Fields
+ */
+
+/**
+ * Main plugin file. Will always be loaded.
+ */
+require_once __DIR__ . '/../secure-custom-fields.php';
diff --git a/composer.json b/composer.json
index 90782be8..92d5c9ce 100644
--- a/composer.json
+++ b/composer.json
@@ -71,6 +71,7 @@
             "@test:phpstan"
         ],
         "test:php": "phpunit",
-        "test:phpstan": "phpstan analyze --memory-limit=2G"
+        "test:phpstan": "phpstan analyze --memory-limit=2G",
+        "test:phpstan:baseline": "phpstan analyze --memory-limit=2G --generate-baseline=bin/baseline.neon"
     }
 }
diff --git a/phpstan.neon b/phpstan.neon
index d162804d..79801a84 100644
--- a/phpstan.neon
+++ b/phpstan.neon
@@ -11,3 +11,5 @@ parameters:
 		- docs
 		- lang
 		- wordpress
+	bootstrapFiles:
+		- bin/phpstan-bootstrap.php
diff --git a/secure-custom-fields.php b/secure-custom-fields.php
index 803b9202..47b17204 100644
--- a/secure-custom-fields.php
+++ b/secure-custom-fields.php
@@ -28,8 +28,6 @@
 	 */
 	#[AllowDynamicProperties]
 	class ACF {
-
-
 		/**
 		 * The plugin version number.
 		 *
@@ -77,14 +75,14 @@ public function __construct() {
 		public function initialize() {
 
 			// Define constants.
-			$this->define( 'ACF', true );
-			$this->define( 'ACF_PATH', plugin_dir_path( __FILE__ ) );
-			$this->define( 'ACF_BASENAME', plugin_basename( __FILE__ ) );
-			$this->define( 'ACF_VERSION', $this->version );
-			$this->define( 'ACF_MAJOR_VERSION', 6 );
-			$this->define( 'ACF_FIELD_API_VERSION', 5 );
-			$this->define( 'ACF_UPGRADE_VERSION', '5.5.0' ); // Highest version with an upgrade routine. See upgrades.php.
-			$this->define( 'ACF_PRO', true );
+			defined( 'ACF' ) || define( 'ACF', true );
+			defined( 'ACF_PATH' ) || define( 'ACF_PATH', plugin_dir_path( __FILE__ ) );
+			defined( 'ACF_BASENAME' ) || define( 'ACF_BASENAME', plugin_basename( __FILE__ ) );
+			defined( 'ACF_VERSION' ) || define( 'ACF_VERSION', $this->version );
+			defined( 'ACF_MAJOR_VERSION' ) || define( 'ACF_MAJOR_VERSION', 6 );
+			defined( 'ACF_FIELD_API_VERSION' ) || define( 'ACF_FIELD_API_VERSION', 5 );
+			defined( 'ACF_UPGRADE_VERSION' ) || define( 'ACF_UPGRADE_VERSION', '5.5.0' ); // Highest version with an upgrade routine. See upgrades.php.
+			defined( 'ACF_PRO' ) || define( 'ACF_PRO', true );
 
 			// Register activation hook.
 			register_activation_hook( __FILE__, array( $this, 'acf_plugin_activated' ) );
@@ -585,14 +583,15 @@ public function posts_where( $where, $wp_query ) {
 		/**
 		 * Defines a constant if doesnt already exist.
 		 *
-		 * @date    3/5/17
 		 * @since   ACF 5.5.13
+		 * @deprecated 6.5.0 -- Use vanilla PHP defined() || define() instead.
 		 *
 		 * @param   string $name  The constant name.
 		 * @param   mixed  $value The constant value.
 		 * @return  void
 		 */
 		public function define( $name, $value = true ) {
+			_deprecated_function( __METHOD__, '6.5.0', 'defined() || define()' );
 			if ( ! defined( $name ) ) {
 				define( $name, $value );
 			}