diff --git a/gnpy/core/info.py b/gnpy/core/info.py
index 05c665156..1fcb60e46 100644
--- a/gnpy/core/info.py
+++ b/gnpy/core/info.py
@@ -11,7 +11,7 @@
 from __future__ import annotations
 from collections import namedtuple
 from collections.abc import Iterable
-from typing import Union, List
+from typing import Union, List, Optional
 from dataclasses import dataclass
 from numpy import argsort, mean, array, append, ones, ceil, any, zeros, outer, full, ndarray, asarray
 
@@ -325,7 +325,7 @@ def is_in_band(frequency: float, band: dict) -> bool:
     return False
 
 
-def demuxed_spectral_information(input_si: SpectralInformation, band: dict) -> SpectralInformation:
+def demuxed_spectral_information(input_si: SpectralInformation, band: dict) -> Optional[SpectralInformation]:
     """extract a si based on band
     """
     filtered_indices = [i for i, f in enumerate(input_si.frequency)
diff --git a/gnpy/core/network.py b/gnpy/core/network.py
index c03c45e34..ada3eecb5 100644
--- a/gnpy/core/network.py
+++ b/gnpy/core/network.py
@@ -368,7 +368,7 @@ def compute_band_power_deviation_and_tilt(srs_power_deviation, design_bands: dic
     return deviation_db, tilt_target
 
 
-def compute_tilt_using_previous_and_next_spans(prev_node, next_node, design_bands: List[str],
+def compute_tilt_using_previous_and_next_spans(prev_node, next_node, design_bands: Dict[str, float],
         input_powers: Dict[str, float], equipment: dict, network: DiGraph, prev_weight: float = 1.0,
         next_weight: float = 0) -> Tuple[Dict[str, float], Dict[str, float]]:
     """Compute the power deviation per band and the tilt target based on previous and next spans.