diff --git a/docs/src/conf.py b/docs/src/conf.py
index d0d0a8249..39a260115 100644
--- a/docs/src/conf.py
+++ b/docs/src/conf.py
@@ -140,7 +140,7 @@ def setup(app):
 }
 
 intersphinx_mapping = {
-    "ase": ("https://wiki.fysik.dtu.dk/ase/", None),
+    "ase": ("https://docs.ase-lib.org/", None),
     "chemfiles": ("https://chemfiles.org/chemfiles.py/latest/", None),
     "metatensor": ("https://docs.metatensor.org/latest/", None),
     "matplotlib": ("https://matplotlib.org/stable/", None),
diff --git a/python/featomic/featomic/calculator_base.py b/python/featomic/featomic/calculator_base.py
index f4b1220cb..c305f225c 100644
--- a/python/featomic/featomic/calculator_base.py
+++ b/python/featomic/featomic/calculator_base.py
@@ -78,10 +78,10 @@ def _options_to_c(
         # nothing to do, all pointers are already NULL
         pass
     elif isinstance(selected_samples, Labels):
-        c_options.selected_samples.subset = selected_samples._as_mts_labels_t()
+        c_options.selected_samples.subset = selected_samples.as_mts_labels_t()
         c_options.__keepalive["selected_samples"] = selected_samples
     elif isinstance(selected_samples, TensorMap):
-        c_options.selected_samples.predefined = selected_samples._ptr
+        c_options.selected_samples.predefined = selected_samples.as_mts_tensormap_t()
     else:
         raise ValueError(
             "expected selected samples to be either an `metatensor.Labels` "
@@ -93,10 +93,12 @@ def _options_to_c(
         # nothing to do, all pointers are already NULL
         pass
     elif isinstance(selected_properties, Labels):
-        c_options.selected_properties.subset = selected_properties._as_mts_labels_t()
+        c_options.selected_properties.subset = selected_properties.as_mts_labels_t()
         c_options.__keepalive["selected_properties"] = selected_properties
     elif isinstance(selected_properties, TensorMap):
-        c_options.selected_properties.predefined = selected_properties._ptr
+        c_options.selected_properties.predefined = (
+            selected_properties.as_mts_tensormap_t()
+        )
     else:
         raise ValueError(
             "expected selected properties to be either an `metatensor.Labels` "
@@ -108,7 +110,7 @@ def _options_to_c(
         # nothing to do, all pointers are already NULL
         pass
     elif isinstance(selected_keys, Labels):
-        c_options.selected_keys = selected_keys._as_mts_labels_t()
+        c_options.selected_keys = selected_keys.as_mts_labels_t()
         c_options.__keepalive["selected_keys"] = selected_keys
     return c_options
 
@@ -308,4 +310,4 @@ def compute(
             self, tensor_map_ptr, c_systems, c_systems._length_, c_options
         )
 
-        return TensorMap._from_ptr(tensor_map_ptr)
+        return TensorMap.unsafe_from_ptr(tensor_map_ptr)