diff --git a/includes/validation/class-amp-validation-error-taxonomy.php b/includes/validation/class-amp-validation-error-taxonomy.php
index 7053526e09c..3c87764aab9 100644
--- a/includes/validation/class-amp-validation-error-taxonomy.php
+++ b/includes/validation/class-amp-validation-error-taxonomy.php
@@ -3303,7 +3303,9 @@ static function ( $attribute_name ) {
 					return sprintf(
 						/* translators: %1$s is the invalid attribute value, %2$s is the attribute name */
 						esc_html__( 'Invalid value %1$s for attribute %2$s', 'amp' ),
-						'<code>' . esc_html( $validation_error['node_attributes'][ $validation_error['attribute'] ] ) . '</code>',
+						empty( $validation_error['node_attributes'][ $validation_error['attribute'] ] )
+							? esc_html__( '(empty)', 'amp' )
+							: '<code>' . esc_html( $validation_error['node_attributes'][ $validation_error['attribute'] ] ) . '</code>',
 						'<code>' . esc_html( $validation_error['attribute'] ) . '</code>'
 					);
 				} else {