diff --git a/src/CSET/recipes/surface_fields/land_mask_for_surface_domain_mean_time_series.yaml b/src/CSET/recipes/surface_fields/land_mask_for_surface_domain_mean_time_series.yaml
index 51fb8d1c3..c8621d35f 100644
--- a/src/CSET/recipes/surface_fields/land_mask_for_surface_domain_mean_time_series.yaml
+++ b/src/CSET/recipes/surface_fields/land_mask_for_surface_domain_mean_time_series.yaml
@@ -10,6 +10,7 @@ steps:
     model_names: $MODEL_NAME
     subarea_type: $SUBAREA_TYPE
     subarea_extent: $SUBAREA_EXTENT
+    constraint: [$VARNAME, "land_binary_mask"]
 
   - operator: filters.apply_mask
     original_field:
diff --git a/src/CSET/recipes/surface_fields/sea_mask_for_surface_domain_mean_time_series.yaml b/src/CSET/recipes/surface_fields/sea_mask_for_surface_domain_mean_time_series.yaml
index bfc42f11e..4056255dc 100644
--- a/src/CSET/recipes/surface_fields/sea_mask_for_surface_domain_mean_time_series.yaml
+++ b/src/CSET/recipes/surface_fields/sea_mask_for_surface_domain_mean_time_series.yaml
@@ -10,6 +10,7 @@ steps:
     model_names: $MODEL_NAME
     subarea_type: $SUBAREA_TYPE
     subarea_extent: $SUBAREA_EXTENT
+    constraint: [$VARNAME, "land_binary_mask"]
 
   - operator: filters.apply_mask
     original_field: