diff --git a/db/extsort.cpp b/db/extsort.cpp
index 3601b52d4d0..e76bc13f958 100644
--- a/db/extsort.cpp
+++ b/db/extsort.cpp
@@ -52,7 +52,8 @@ namespace mongo {
             _cur = 0;
         }
         
-        remove_all( _root );
+        unsigned long removed = remove_all( _root );
+        wassert( removed == 1 + _files.size() );
     }
 
     void BSONObjExternalSorter::sort(){