diff --git a/composer.json b/composer.json
index e9d4435a..00792969 100644
--- a/composer.json
+++ b/composer.json
@@ -15,14 +15,15 @@
         "wp-cli/wp-cli": "^2.12"
     },
     "require-dev": {
-        "wp-cli/wp-cli-tests": "^4"
+        "wp-cli/wp-cli-tests": "^5"
     },
     "config": {
         "process-timeout": 7200,
         "sort-packages": true,
         "allow-plugins": {
             "dealerdirect/phpcodesniffer-composer-installer": true,
-            "johnpbloch/wordpress-core-installer": true
+            "johnpbloch/wordpress-core-installer": true,
+            "phpstan/extension-installer": true
         },
         "lock": false
     },
@@ -59,12 +60,14 @@
         "behat-rerun": "rerun-behat-tests",
         "lint": "run-linter-tests",
         "phpcs": "run-phpcs-tests",
+        "phpstan": "run-phpstan-tests",
         "phpunit": "run-php-unit-tests",
         "phpcbf": "run-phpcbf-cleanup",
         "prepare-tests": "install-package-tests",
         "test": [
             "@lint",
             "@phpcs",
+            "@phpstan",
             "@phpunit",
             "@behat"
         ]
diff --git a/phpstan.neon.dist b/phpstan.neon.dist
new file mode 100644
index 00000000..ca9e0ea4
--- /dev/null
+++ b/phpstan.neon.dist
@@ -0,0 +1,13 @@
+parameters:
+  level: 9
+  paths:
+    - src
+    - role-command.php
+  scanDirectories:
+    - vendor/wp-cli/wp-cli/php
+  scanFiles:
+    - vendor/php-stubs/wordpress-stubs/wordpress-stubs.php
+  treatPhpDocTypesAsCertain: false
+  ignoreErrors:
+    - identifier: missingType.parameter
+    - identifier: missingType.return
diff --git a/src/Capabilities_Command.php b/src/Capabilities_Command.php
index e27a0cb1..97db2033 100644
--- a/src/Capabilities_Command.php
+++ b/src/Capabilities_Command.php
@@ -26,7 +26,7 @@ class Capabilities_Command extends WP_CLI_Command {
 	/**
 	 * List of available fields.
 	 *
-	 * @var array
+	 * @var array<string>
 	 */
 	private $fields = [ 'name' ];
 
diff --git a/src/Role_Command.php b/src/Role_Command.php
index 0fe78d58..a029d2a3 100644
--- a/src/Role_Command.php
+++ b/src/Role_Command.php
@@ -42,14 +42,14 @@ class Role_Command extends WP_CLI_Command {
 	/**
 	 * List of available fields.
 	 *
-	 * @var array
+	 * @var array<string>
 	 */
 	private $fields = [ 'name', 'role' ];
 
 	/**
 	 * Default roles as provided by WordPress Core.
 	 *
-	 * @var array
+	 * @var array<string>
 	 */
 	private $roles = [ 'administrator', 'editor', 'author', 'contributor', 'subscriber' ];
 
@@ -347,13 +347,17 @@ public function reset( $args, $assoc_args ) {
 				remove_role( $role );
 			}
 
+			/**
+			 * @var array<string|\WP_Role> $preserve
+			 */
+
 			// Put back all default roles and capabilities.
 			populate_roles();
 
 			// Restore the preserved roles.
 			foreach ( $preserve as $k => $roleobj ) {
 				// Re-remove after populating.
-				if ( is_a( $roleobj, 'WP_Role' ) ) {
+				if ( $roleobj instanceof \WP_Role ) {
 					remove_role( $roleobj->name );
 					add_role( $roleobj->name, ucwords( $roleobj->name ), $roleobj->capabilities );
 				} else {
@@ -373,13 +377,15 @@ public function reset( $args, $assoc_args ) {
 			if ( $after[ $role_key ] != $before[ $role_key ] ) {
 				++$num_reset;
 				$before_capabilities = isset( $before[ $role_key ] ) ? $before[ $role_key ]->capabilities : [];
-				$restored_cap        = array_diff_key( $after[ $role_key ]->capabilities, $before_capabilities );
-				$removed_cap         = array_diff_key( $before_capabilities, $after[ $role_key ]->capabilities );
-				$restored_cap_count  = count( $restored_cap );
-				$removed_cap_count   = count( $removed_cap );
-				$restored_text       = ( 1 === $restored_cap_count ) ? '%d capability' : '%d capabilities';
-				$removed_text        = ( 1 === $removed_cap_count ) ? '%d capability' : '%d capabilities';
-				$message             = "Restored {$restored_text} to and removed {$removed_text} from '%s' role.";
+				// @phpstan-ignore property.nonObject
+				$restored_cap = array_diff_key( $after[ $role_key ]->capabilities, $before_capabilities );
+				// @phpstan-ignore property.nonObject
+				$removed_cap        = array_diff_key( $before_capabilities, $after[ $role_key ]->capabilities );
+				$restored_cap_count = count( $restored_cap );
+				$removed_cap_count  = count( $removed_cap );
+				$restored_text      = ( 1 === $restored_cap_count ) ? '%d capability' : '%d capabilities';
+				$removed_text       = ( 1 === $removed_cap_count ) ? '%d capability' : '%d capabilities';
+				$message            = "Restored {$restored_text} to and removed {$removed_text} from '%s' role.";
 				WP_CLI::log( sprintf( $message, $restored_cap_count, $removed_cap_count, $role_key ) );
 			} else {
 				WP_CLI::log( "No changes necessary for '{$role_key}' role." );