diff --git a/src/infrastructure/cache/PhutilAPCKeyValueCache.php b/src/infrastructure/cache/PhutilAPCKeyValueCache.php
--- a/src/infrastructure/cache/PhutilAPCKeyValueCache.php
+++ b/src/infrastructure/cache/PhutilAPCKeyValueCache.php
@@ -44,6 +44,10 @@
       $is_apcu = self::isAPCu();
     }
 
+    if ($ttl === null) {
+      $ttl = 0;
+    }
+
     // NOTE: Although modern APC supports passing an array to `apc_store()`,
     // it is not supported by older version of APC or by HPHP.