diff --git a/src/wp-includes/abilities-api/class-wp-ability.php b/src/wp-includes/abilities-api/class-wp-ability.php
index d116080c1ccdc..2b18b93a7d1cb 100644
--- a/src/wp-includes/abilities-api/class-wp-ability.php
+++ b/src/wp-includes/abilities-api/class-wp-ability.php
@@ -445,10 +445,18 @@ public function normalize_input( $input = null ) {
 		}
 
 		$input_schema = $this->get_input_schema();
-		if ( ! empty( $input_schema ) && array_key_exists( 'default', $input_schema ) ) {
-			return $input_schema['default'];
+		// This tries to compute a default value from the input schema properties.
+		// It is a very basic implementation and does not cover all JSON Schema features.
+		// It only looks for `default` values in the top-level `properties`.
+		if ( ! empty( $input_schema ) && array_key_exists( 'properties', $input_schema ) ) {
+			$result = array(); 
+			foreach ( $input_schema['properties'] as $property_name => $property_schema ) {
+				if ( array_key_exists( 'default', $property_schema ) ) {
+					$result[ $property_name ] = $property_schema['default'];
+				}
+			}
+			return $result;
 		}
-
 		return null;
 	}
 
diff --git a/src/wp-includes/abilities.php b/src/wp-includes/abilities.php
index c71eeb158a304..a36d51b5224d4 100644
--- a/src/wp-includes/abilities.php
+++ b/src/wp-includes/abilities.php
@@ -96,11 +96,11 @@ function wp_register_core_abilities(): void {
 							'type' => 'string',
 							'enum' => $site_info_fields,
 						),
+						'default'              =>  array(),
 						'description' => __( 'Optional: Limit response to specific fields. If omitted, all fields are returned.' ),
 					),
 				),
 				'additionalProperties' => false,
-				'default'              => array(),
 			),
 			'output_schema'       => array(
 				'type'                 => 'object',