diff --git a/classes/Memcached_DataObject.php b/classes/Memcached_DataObject.php
index 4579f64df8..a7fec365e0 100644
--- a/classes/Memcached_DataObject.php
+++ b/classes/Memcached_DataObject.php
@@ -593,7 +593,7 @@ class Memcached_DataObject extends Safe_DataObject
         return $c->get($cacheKey);
     }
 
-    static function cacheSet($keyPart, $value)
+    static function cacheSet($keyPart, $value, $flag=null, $expiry=null)
     {
         $c = self::memcache();
 
@@ -603,7 +603,7 @@ class Memcached_DataObject extends Safe_DataObject
 
         $cacheKey = common_cache_key($keyPart);
 
-        return $c->set($cacheKey, $value);
+        return $c->set($cacheKey, $value, $flag, $expiry);
     }
 
     static function valueString($v)
diff --git a/plugins/Sitemap/Sitemap_notice_count.php b/plugins/Sitemap/Sitemap_notice_count.php
index 2a375b3e48..6e0061e97b 100644
--- a/plugins/Sitemap/Sitemap_notice_count.php
+++ b/plugins/Sitemap/Sitemap_notice_count.php
@@ -153,7 +153,9 @@ class Sitemap_notice_count extends Memcached_DataObject
                 $noticeCounts[$snc->notice_date] = $snc->notice_count;
             }
 
-            self::cacheSet('sitemap:notice:counts', $noticeCounts);
+            // Cache notice counts for 4 hours.
+
+            self::cacheSet('sitemap:notice:counts', $noticeCounts, null, time() + 4 * 60 * 60);
         }
 
         return $noticeCounts;
diff --git a/plugins/Sitemap/Sitemap_user_count.php b/plugins/Sitemap/Sitemap_user_count.php
index 64b4c34428..98dd05bfed 100644
--- a/plugins/Sitemap/Sitemap_user_count.php
+++ b/plugins/Sitemap/Sitemap_user_count.php
@@ -154,7 +154,9 @@ class Sitemap_user_count extends Memcached_DataObject
                 $userCounts[$suc->registration_date] = $suc->user_count;
             }
 
-            self::cacheSet('sitemap:user:counts', $userCounts);
+            // Cache user counts for 4 hours.
+
+            self::cacheSet('sitemap:user:counts', $userCounts, null, time() + 4 * 60 * 60);
         }
 
         return $userCounts;