diff --git a/src/sleplet/meshes/_mesh_slepian_decomposition.py b/src/sleplet/meshes/_mesh_slepian_decomposition.py
index 0bace0232..80ae12644 100644
--- a/src/sleplet/meshes/_mesh_slepian_decomposition.py
+++ b/src/sleplet/meshes/_mesh_slepian_decomposition.py
@@ -92,15 +92,16 @@ def _harmonic_sum(self, rank: int) -> float:
 
     def _detect_method(self) -> None:
         """Detects what method is used to perform the decomposition."""
-        if isinstance(self.u_i, np.ndarray):
+        if self.u_i is not None:
             _logger.info("harmonic sum method selected")
             self.method = "harmonic_sum"
-        elif isinstance(self.u, np.ndarray) and not self.mask:
-            _logger.info("integrating the whole mesh method selected")
-            self.method = "integrate_mesh"
-        elif isinstance(self.u, np.ndarray):
-            _logger.info("integrating a region on the mesh method selected")
-            self.method = "integrate_region"
+        elif self.u is not None:
+            if self.mask:
+                _logger.info("integrating a region on the mesh method selected")
+                self.method = "integrate_region"
+            else:
+                _logger.info("integrating the whole mesh method selected")
+                self.method = "integrate_mesh"
         else:
             raise RuntimeError(
                 "need to pass one off harmonic coefficients, real pixels "
diff --git a/src/sleplet/slepian/_slepian_decomposition.py b/src/sleplet/slepian/_slepian_decomposition.py
index 518382f11..223a8e72c 100644
--- a/src/sleplet/slepian/_slepian_decomposition.py
+++ b/src/sleplet/slepian/_slepian_decomposition.py
@@ -98,15 +98,16 @@ def _harmonic_sum(self, rank: int) -> complex:
 
     def _detect_method(self) -> None:
         """Detects what method is used to perform the decomposition."""
-        if isinstance(self.flm, np.ndarray):
+        if self.flm is not None:
             _logger.info("harmonic sum method selected")
             self.method = "harmonic_sum"
-        elif isinstance(self.f, np.ndarray) and not isinstance(self.mask, np.ndarray):
-            _logger.info("integrating the whole sphere method selected")
-            self.method = "integrate_sphere"
-        elif isinstance(self.f, np.ndarray):
-            _logger.info("integrating a region on the sphere method selected")
-            self.method = "integrate_region"
+        elif self.f is not None:
+            if self.mask is None:
+                _logger.info("integrating the whole sphere method selected")
+                self.method = "integrate_sphere"
+            else:
+                _logger.info("integrating a region on the sphere method selected")
+                self.method = "integrate_region"
         else:
             raise RuntimeError(
                 "need to pass one off harmonic coefficients, real pixels "