diff -u b/platform/backup.provision.inc b/platform/backup.provision.inc
--- b/platform/backup.provision.inc
+++ b/platform/backup.provision.inc
@@ -10,7 +10,6 @@
   './files/css',
   './files/js',
   './private/temp',
-  './.git',
 );
 
 /**
@@ -131,8 +130,11 @@
 }
 
 function drush_provision_drupal_provision_backup_get_exclusions() {
+  $directories = PROVISION_BACKUP_EXCLUDED_DIRECTORIES;
+  drush_command_invoke_all_ref('provision_backup_exclusions_alter', $directories);
+
   $exclusions = "";
-  foreach (PROVISION_BACKUP_EXCLUDED_DIRECTORIES as $directory) {
+  foreach ($directories as $directory) {
     $exclusions .= " --exclude='$directory'";
   }
   return $exclusions;
only in patch2:
unchanged:
--- a/provision.api.php
+++ b/provision.api.php
@@ -473,4 +473,18 @@ ENV;
 
   // Hide sensitive information from any other users.
   provision_file()->chmod($file_name, 0400);
-}
\ No newline at end of file
+}
+
+/**
+ * Alter the list of directories excluded from site backups.
+ *
+ * @param $directories
+ *   An array of strings representing directories, which are relative to a
+ *   site directory.
+ *
+ * @see drush_provision_drupal_provision_backup_get_exclusions()
+ */
+function hook_provision_backup_exclusions_alter(&$directories) {
+  // Prevent backing up the CiviCRM Smarty cache.
+  $directories[] = './files/civicrm/templates_c';
+}