diff --git a/src/atom_vec_hybrid.cpp b/src/atom_vec_hybrid.cpp
index 8a371c6aa3..0f9bfdbf73 100644
--- a/src/atom_vec_hybrid.cpp
+++ b/src/atom_vec_hybrid.cpp
@@ -331,6 +331,7 @@ int AtomVecHybrid::pack_exchange(int i, double *buf)
     for (int iextra = 0; iextra < atom->nextra_grow; iextra++) 
       m += modify->fix[atom->extra_grow[iextra]]->pack_exchange(i,&buf[m]);
 
+  buf[0] = m;
   return m;
 }