diff --git a/wp-includes/load.php b/wp-includes/load.php
index 3fc74006a0..8cc14e06db 100644
--- a/wp-includes/load.php
+++ b/wp-includes/load.php
@@ -138,7 +138,8 @@ function wp_check_php_mysql_versions() {
  * If not set, the type defaults to 'production'.
  *
  * @since 5.5.0
- * @since 5.5.1 The 'local' type was added.
+ * @since 5.5.1 Added the 'local' type.
+ * @since 5.5.1 Removed the ability to alter the list of types.
  *
  * @return string The current environment type.
  */
@@ -156,17 +157,20 @@ function wp_get_environment_type() {
 		'production',
 	);
 
-	// Check if the environment variable has been set, if `getenv` is available on the system.
-	if ( function_exists( 'getenv' ) ) {
-		$has_env = getenv( 'WP_ENVIRONMENT_TYPES' );
-		if ( false !== $has_env ) {
-			$wp_environments = explode( ',', $has_env );
+	// Add a note about the deprecated WP_ENVIRONMENT_TYPES constant.
+	if ( defined( 'WP_ENVIRONMENT_TYPES' ) && function_exists( '_deprecated_argument' ) ) {
+		if ( function_exists( '__' ) ) {
+			/* translators: %s: WP_ENVIRONMENT_TYPES */
+			$message = sprintf( __( 'The %s constant is no longer supported.' ), 'WP_ENVIRONMENT_TYPES' );
+		} else {
+			$message = sprintf( 'The %s constant is no longer supported.', 'WP_ENVIRONMENT_TYPES' );
 		}
-	}
 
-	// Fetch the environment types from a constant, this overrides the global system variable.
-	if ( defined( 'WP_ENVIRONMENT_TYPES' ) ) {
-		$wp_environments = WP_ENVIRONMENT_TYPES;
+		_deprecated_argument(
+			'define()',
+			'5.5.1',
+			$message
+		);
 	}
 
 	// Check if the environment variable has been set, if `getenv` is available on the system.
diff --git a/wp-includes/version.php b/wp-includes/version.php
index 6bac2d9b0d..8ae614d98d 100644
--- a/wp-includes/version.php
+++ b/wp-includes/version.php
@@ -13,7 +13,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '5.5.1-alpha-48893';
+$wp_version = '5.5.1-alpha-48896';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.