diff --git a/src/chain-complexes.lisp b/src/chain-complexes.lisp
index c61421e..da70a8a 100644
--- a/src/chain-complexes.lisp
+++ b/src/chain-complexes.lisp
@@ -219,7 +219,7 @@
 					       :adjustable t
 					       :fill-pointer 0))
                                (make-list +maximal-dimension+)))
-		   (:cmbn nil)))
+		   (:cmbn (make-array 0))))
 	   (push mrph *mrph-list*)
 	   mrph))))