diff --git a/src/index/index.lisp b/src/index/index.lisp
index 8e147c6..6a29f00 100644
--- a/src/index/index.lisp
+++ b/src/index/index.lisp
@@ -351,18 +351,19 @@
   (num-docs (reader self)))
 
 (defmethod add-indexes ((self index) &rest indexes)
-  (when (> (length indexes) 0)
-    (when (typep (elt indexes 0) 'index)
-      (setf indexes (map 'vector #'reader indexes)))
-    (cond ((typep (elt indexes 0) 'index-reader)
-	   (let ((reader (reader self)))
-	     (setf indexes (remove reader indexes)))
-	   (add-indexes-readers (writer self) indexes))
-	  ((typep (elt indexes 0) 'directory)
-	   (setf indexes (remove (slot-value self 'dir) indexes))
-	   (apply #'add-indexes (writer self) indexes))
-	  (T
-	   (error "Unknown index type ~S when trying to merge indexes." (elt indexes 0))))))
+  (let ((indexes indexes))
+    (when (> (length indexes) 0)
+      (when (typep (elt indexes 0) 'index)
+        (setf indexes (map 'vector #'reader indexes)))
+      (cond ((typep (elt indexes 0) 'index-reader)
+             (let ((reader (reader self)))
+               (setf indexes (remove reader indexes)))
+             (add-indexes-readers (writer self) indexes))
+            ((typep (elt indexes 0) 'directory)
+             (setf indexes (remove (slot-value self 'dir) indexes))
+             (apply #'add-indexes (writer self) indexes))
+            (T
+             (error "Unknown index type ~S when trying to merge indexes." (elt indexes 0)))))))
 
 (defgeneric persist (index directory &key create-p))