diff --git modules/system/system.api.php modules/system/system.api.php
index 1356dd6..3f63ce0 100644
--- modules/system/system.api.php
+++ modules/system/system.api.php
@@ -3844,12 +3844,14 @@ function hook_date_formats() {
 /**
  * Alter date formats declared by another module.
  *
- * Called by _system_date_format_types_build() to allow modules to alter the
- * return values from implementations of hook_date_formats().
+ * Called by _system_date_formats_build() to allow modules to alter the return
+ * values from implementations of hook_date_formats().
  */
-function hook_date_formats_alter(&$formats) {
-  foreach ($formats as $id => $format) {
-    $formats[$id]['locales'][] = 'en-ca';
+function hook_date_formats_alter(&$types) {
+  foreach ($types as $type => &$formats) {
+    foreach ($formats as $id => &$format) {
+      $format['locales'][] = 'en-ca';
+    }
   }
 }