diff --git a/src/cipsi/run_pt2_slave.irp.f b/src/cipsi/run_pt2_slave.irp.f
index ff048d95..b6545922 100644
--- a/src/cipsi/run_pt2_slave.irp.f
+++ b/src/cipsi/run_pt2_slave.irp.f
@@ -113,7 +113,7 @@ subroutine run_pt2_slave_small(thread,iproc,energy)
       call create_selection_buffer(bsize, bsize*2, b)
       buffer_ready = .True.
     else
-      ASSERT (N == b%N)
+      ASSERT (b%N == bsize)
     endif
 
     double precision :: time0, time1