diff --git a/src/grid_mod.F90 b/src/grid_mod.F90
index 437d5da079223c82f591a1d4193ca7327d34733e..139cd0abe9a60444394d846263bcadad61a73266 100644
--- a/src/grid_mod.F90
+++ b/src/grid_mod.F90
@@ -405,6 +405,7 @@ CONTAINS
 
   SUBROUTINE set_zgrid
     USE prec_const
+    USE model, ONLY: mu_z
     IMPLICIT NONE
     INTEGER :: i_, fid
     REAL    :: grid_shift, Lz