diff --git a/core/includes/common.inc b/core/includes/common.inc
index 91e150e..930f7b0 100644
--- a/core/includes/common.inc
+++ b/core/includes/common.inc
@@ -631,6 +631,17 @@ function valid_url($url, $absolute = FALSE) {
  *
  * @see \Drupal\Component\Utility\Number::validStep()
  *
+ * @param numeric $value
+ *   The value that needs to be checked.
+ * @param numeric $step
+ *   The step scale factor. Must be positive.
+ * @param numeric $offset
+ *   (optional) An offset, to which the difference must be a multiple of the
+ *   given step.
+ *
+ * @return bool
+ *   TRUE if no step mismatch has occured, or FALSE otherwise.
+ *
  * @deprecated as of Drupal 8.0. Use
  *   \Drupal\Component\Utility\Number::validStep() directly instead
  */