diff --git a/src/acct/watch_helper.rb b/src/acct/watch_helper.rb
index 93ab3d56d3..4cc5ab9c98 100644
--- a/src/acct/watch_helper.rb
+++ b/src/acct/watch_helper.rb
@@ -338,7 +338,7 @@ module WatchHelper
             VmSample.multi_insert(@@samples_cache)
 
             Vm.each { |vm|
-                if vm.samples.count > @@vm_window_size -1
+                if vm.samples.count > @@vm_window_size
                     vm.samples.last.delete
                 end
             }