diff --git a/flow360/component/simulation/meshing_param/face_params.py b/flow360/component/simulation/meshing_param/face_params.py
index b41df3f2d..f0570c20d 100644
--- a/flow360/component/simulation/meshing_param/face_params.py
+++ b/flow360/component/simulation/meshing_param/face_params.py
@@ -78,9 +78,9 @@ class GeometryRefinement(Flow360BaseModel):
         + "to geometry_accuracy should be resolved accurately during the surface meshing process.",
     )
 
-    sealing_size: Optional[LengthType.NonNegative] = pd.Field(
+    sealing_size: LengthType.NonNegative = pd.Field(
         0.0 * u.m,
-        description="Threshold size below which all geometry gaps are automatically closed. Zero is deactivated.",
+        description="Threshold size below which all geometry gaps are automatically closed.",
     )
 
     # Note: No checking on deleted surfaces since geometry accuracy on deleted surface does impact the volume mesh.
diff --git a/flow360/component/simulation/meshing_param/params.py b/flow360/component/simulation/meshing_param/params.py
index 6c1ee3b8e..cac79cfee 100644
--- a/flow360/component/simulation/meshing_param/params.py
+++ b/flow360/component/simulation/meshing_param/params.py
@@ -168,10 +168,10 @@ class MeshingDefaults(Flow360BaseModel):
         + "This can be overridden with class: ~flow360.GeometryRefinement",
     )
 
-    sealing_size: Optional[LengthType.NonNegative] = pd.Field(
+    sealing_size: LengthType.NonNegative = pd.Field(
         0.0 * u.m,
         description="Threshold size below which all geometry gaps are automatically closed. "
-        + "Zero is deactivated. This can be overridden with class: ~flow360.GeometryRefinement",
+        + "This can be overridden with class: ~flow360.GeometryRefinement",
     )
 
     @pd.field_validator("number_of_boundary_layers", mode="after")