diff --git a/sources/coordinates.F90 b/sources/coordinates.F90
index ff55ed3..67f62d9 100644
--- a/sources/coordinates.F90
+++ b/sources/coordinates.F90
@@ -59,8 +59,8 @@ module coordinates
 
 ! block interior and ghost zone indices
 !
-  integer     , save :: nbl =  2, nb  =  3, nbu =  4
-  integer     , save :: nel =  9, ne  = 10, neu = 11
+  integer     , save :: nbl =  2, nb  =  3, nbu =  4, nbm =  2, nbp =  4
+  integer     , save :: nel =  9, ne  = 10, neu = 11, nem =  9, nep = 11
 
 ! the domain bounds
 !
@@ -279,6 +279,10 @@ module coordinates
     nbu = nb + ng - 1
     nel = ne - ng + 1
     neu = ne + 1
+    nbm = nb - 1
+    nem = ne - 1
+    nbp = nb + 1
+    nep = ne + 1
 
 ! determine domain periodicity
 !