diff --git a/linopy/common.py b/linopy/common.py
index 279bb5c6..0823deac 100644
--- a/linopy/common.py
+++ b/linopy/common.py
@@ -287,6 +287,16 @@ def as_dataarray(
 
 
 def broadcast_mask(mask: DataArray, labels: DataArray) -> DataArray:
+    """
+    Broadcast a boolean mask to match the shape of labels.
+
+    Ensures that mask dimensions are a subset of labels dimensions, broadcasts
+    the mask accordingly, and fills any NaN values (from missing coordinates)
+    with False while emitting a FutureWarning.
+    """
+    assert set(mask.dims).issubset(labels.dims), (
+        "Dimensions of mask not a subset of resulting labels dimensions."
+    )
     mask = mask.broadcast_like(labels)
     if mask.isnull().any():
         warn(
diff --git a/linopy/model.py b/linopy/model.py
index a58e09e5..d5d4830a 100644
--- a/linopy/model.py
+++ b/linopy/model.py
@@ -552,9 +552,6 @@ def add_variables(
 
         if mask is not None:
             mask = as_dataarray(mask, coords=data.coords, dims=data.dims).astype(bool)
-            assert set(mask.dims).issubset(data.dims), (
-                "Dimensions of mask not a subset of resulting labels dimensions."
-            )
             mask = broadcast_mask(mask, data.labels)
 
         # Auto-mask based on NaN in bounds (use numpy for speed)
@@ -750,9 +747,6 @@ def add_constraints(
 
         if mask is not None:
             mask = as_dataarray(mask).astype(bool)
-            assert set(mask.dims).issubset(data.dims), (
-                "Dimensions of mask not a subset of resulting labels dimensions."
-            )
             mask = broadcast_mask(mask, data.labels)
 
         # Auto-mask based on null expressions or NaN RHS (use numpy for speed)
diff --git a/test/test_constraints.py b/test/test_constraints.py
index 0f0ae35a..01aebb69 100644
--- a/test/test_constraints.py
+++ b/test/test_constraints.py
@@ -191,6 +191,11 @@ def test_masked_constraints_broadcast() -> None:
     assert (m.constraints.labels.bc3[2:5, :] == -1).all()
     assert (m.constraints.labels.bc3[5:10, :] == -1).all()
 
+    # Mask with extra dimension not in data should raise
+    mask4 = xr.DataArray([True, False], dims=["extra_dim"])
+    with pytest.raises(AssertionError, match="not a subset"):
+        m.add_constraints(1 * x + 10 * y, EQUAL, 0, name="bc4", mask=mask4)
+
 
 def test_non_aligned_constraints() -> None:
     m: Model = Model()
diff --git a/test/test_variables.py b/test/test_variables.py
index 824ec77a..37de6aff 100644
--- a/test/test_variables.py
+++ b/test/test_variables.py
@@ -134,6 +134,11 @@ def test_variables_mask_broadcast() -> None:
     assert (z.labels[2:5, :] == -1).all()
     assert (z.labels[5:10, :] == -1).all()
 
+    # Mask with extra dimension not in data should raise
+    mask4 = xr.DataArray([True, False], dims=["extra_dim"])
+    with pytest.raises(AssertionError, match="not a subset"):
+        m.add_variables(lower, upper, name="w", mask=mask4)
+
 
 def test_variables_get_name_by_label(m: Model) -> None:
     assert m.variables.get_name_by_label(4) == "x"