diff --git a/extra/memory/piles/piles.factor b/extra/memory/piles/piles.factor
index 651bf2ec6c..46729c42be 100644
--- a/extra/memory/piles/piles.factor
+++ b/extra/memory/piles/piles.factor
@@ -1,5 +1,5 @@
 ! (c)2009 Joe Groff bsd license
-USING: accessors alien destructors kernel libc math ;
+USING: accessors alien alien.c-types destructors kernel libc math ;
 IN: memory.piles
 
 TUPLE: pile