diff --git a/rose-stem/app/generate_weights/bin/common.py b/rose-stem/app/generate_weights/bin/common.py
index 572a4dbe8..745fcbf6e 100755
--- a/rose-stem/app/generate_weights/bin/common.py
+++ b/rose-stem/app/generate_weights/bin/common.py
@@ -140,55 +140,55 @@ def ord2_corr(src_field, src_mask, rank_src):
     """calculate lon and lat gradients to correct
        destination values for conservative
        weights """
-#we need
+    #we need
     src_mask_r = np.reshape(src_mask, (rank_src[1], rank_src[0]))
     grad_lon = np.zeros((rank_src[0]*rank_src[1], 1), dtype=np.float64)
     grad_lat = np.zeros((rank_src[0]*rank_src[1], 1), dtype=np.float64)
-#find unique source grid points
+    #find unique source grid points
     for j in range(rank_src[1]):
         for i in range(rank_src[0]):
             delew = .5
             delsn = .5
             ipt = j*rank_src[0]+i
             if(src_mask_r[j, i]):
-#find N,E,S,W points for col[i], use fortran indexing (starts with 1)
-#follow scrip approach. Incorrect for NEMO grid for global model!
-#find i-1 and i+1
-#i-1
+                #find N,E,S,W points for col[i], use fortran indexing (starts with 1)
+                #follow scrip approach. Incorrect for NEMO grid for global model!
+                #find i-1 and i+1
+                #i-1
                 ipt_m1 = i - 1
                 if ipt_m1 < 0:
                     ipt_m1 = rank_src[0] -1 + ipt_m1
-#account for mask i-1
+                #account for mask i-1
                 if(src_mask_r[j, ipt_m1] == 0):
                     ipt_m1 = i
                     delew = 1.
-#i+1
+                #i+1
                 ipt_p1 = i + 1
                 if ipt_p1 > rank_src[0] -1:
                     ipt_p1 = ipt_p1 - rank_src[1] - 1
-#account for mask i+1
+                #account for mask i+1
                 if(src_mask_r[j, ipt_p1] == 0):
                     ipt_p1 = i
                     delew = 1.
-#j+1
+                #j+1
                 jpt_p1 = j + 1
                 if(jpt_p1 > rank_src[1]) - 1:
                     jpt_p1 = j
                     delsn = 1.
-#account for mask j+1
+                #account for mask j+1
                 if src_mask_r[jpt_p1, i] == 0:
                     jpt_p1 = j
                     delsn = 1.
-#j-1
+                #j-1
                 jpt_m1 = j - 1
                 if jpt_m1 < 0:
                     jpt_m1 = j
                     delsn = 1.
-#account for mask j-1
+                #account for mask j-1
                 if src_mask_r[jpt_m1, i] == 0:
                     jpt_m1 = j
                     delsn = 1.
-#shift index python (0.0) fortran (1,1)
+                #shift index python (0.0) fortran (1,1)
                 ipt_w = j*rank_src[0]+ipt_m1
                 ipt_e = j*rank_src[0]+ipt_p1
                 jpt_n = jpt_p1*rank_src[0]+i
diff --git a/rose-stem/app/generate_weights/bin/generate_weights.py b/rose-stem/app/generate_weights/bin/generate_weights.py
index 45c7e630d..e69fefda0 100755
--- a/rose-stem/app/generate_weights/bin/generate_weights.py
+++ b/rose-stem/app/generate_weights/bin/generate_weights.py
@@ -25,6 +25,7 @@ def __init__(self):
         self.lfric_grid_path = None
         self.um_grid_type = None
         self.um_grid_path = None
+        self.um_mask_value = None
 
     def set_regrid_info(self):
         '''Set information from environment variables'''
@@ -40,6 +41,7 @@ def set_regrid_info(self):
         self.um_grid_path = os.environ.get('GRID_PATH_UM')
         self.lfric_grid_type = os.environ.get('GRID_TYPE_LFRIC')
         self.lfric_grid_path = os.environ.get('GRID_PATH_LFRIC')
+        self.um_mask_value = um_rmdi
 
     def set_arguments_um2lfric(self):
         '''Set ESMF regrid command line options'''
@@ -48,6 +50,8 @@ def set_arguments_um2lfric(self):
         options = options + ' --dst_loc center'
         options = options + ' --64bit_offset --check -m ' + self.method
         options = options + ' --extrap_method neareststod'
+        options = options + ' --src_missingvalue um_mask_value'
+        options = options + ' -v mask_b,dst_grid_imask'
         if self.um_grid_type == 'regional':
             options = options + ' --src_regional '
         if self.lfric_grid_type == 'regional':
@@ -71,6 +75,8 @@ def set_arguments_lfric2um(self):
         options = options + ' --src_loc center'
         options = options + ' -d ' + self.um_grid_path
         options = options + ' --64bit_offset --check -m ' + self.method
+        options = options + ' -v mask_a,src_grid_imask'
+        options = options + ' --dst_missingvalue um_mask_value'
         if self.um_grid_type == 'regional':
             options = options + ' --src_regional '
         if self.lfric_grid_type == 'regional':