diff --git a/basis/specialized-arrays/alien/alien.factor b/basis/specialized-arrays/alien/alien.factor
index 465d1665f9..a2bca17a9a 100644
--- a/basis/specialized-arrays/alien/alien.factor
+++ b/basis/specialized-arrays/alien/alien.factor
@@ -1,4 +1,5 @@
 USE: specialized-arrays.functor
 IN: specialized-arrays.alien
 
-<< "void*" define-array >>
\ No newline at end of file
+<< "void*" define-array >>
+<< "ptrdiff_t" define-array >>