diff --git a/lineage/LineageTree.py b/lineage/LineageTree.py
index 57c6bc8e0..9ce659305 100644
--- a/lineage/LineageTree.py
+++ b/lineage/LineageTree.py
@@ -12,7 +12,7 @@ class LineageTree:
 
     pi: npt.NDArray[np.float64]
     T: npt.NDArray[np.float64]
-    leaves_idx: npt.NDArray[np.uintp]
+    leaves_idx: np.ndarray
     idx_by_gen: list[np.ndarray]
     output_lineage: list[CellVar]
     cell_to_parent: np.ndarray
@@ -26,10 +26,12 @@ def __init__(self, list_of_cells: list, E: list):
         # assign times using the state distribution specific time model
         E[0].assign_times(self.output_lineage)
 
-        self.leaves_idx = get_leaves_idx(self.output_lineage)
         self.cell_to_parent = cell_to_parent(self.output_lineage)
         self.cell_to_daughters = cell_to_daughters(self.output_lineage)
 
+        # Leaves have no daughters
+        self.leaves_idx = np.nonzero(np.all(self.cell_to_daughters == -1, axis=1))[0]
+
     @classmethod
     def rand_init(
         cls,
@@ -227,18 +229,3 @@ def cell_to_daughters(lineage: list[CellVar]) -> np.ndarray:
             output[ii, 1] = lineage.index(cell.right)
 
     return output
-
-
-def get_leaves_idx(lineage: list[CellVar]) -> npt.NDArray[np.uintp]:
-    """
-    A function to find the leaves and their indexes in the lineage list.
-    :param lineage: The list of cells in a lineageTree object.
-    :return leaf_indices: The list of cell indexes.
-    :return leaves: The last cells in the lineage branch.
-    """
-    leaf_indices = []
-    for index, cell in enumerate(lineage):
-        if cell.isLeaf():
-            assert cell.observed
-            leaf_indices.append(index)  # appending the index of the cells
-    return np.array(leaf_indices, dtype=np.uintp)
diff --git a/lineage/states/stateCommon.py b/lineage/states/stateCommon.py
index ef410fc67..1e47eba45 100644
--- a/lineage/states/stateCommon.py
+++ b/lineage/states/stateCommon.py
@@ -2,7 +2,7 @@
 
 import warnings
 import numpy as np
-from numba import njit
+from numba import jit
 from numba.typed import List
 import numpy.typing as npt
 from ctypes import CFUNCTYPE, c_double
@@ -51,7 +51,7 @@ def bern_estimator(bern_obs: np.ndarray, gammas: np.ndarray):
     return numerator / denominator
 
 
-@njit
+@jit(nopython=True)
 def gamma_LL(
     logX: npt.NDArray[np.float64],
     gamma_obs: List[npt.NDArray[np.float64]],
diff --git a/lineage/tests/test_LineageTree.py b/lineage/tests/test_LineageTree.py
index 1a3b25440..395657ade 100644
--- a/lineage/tests/test_LineageTree.py
+++ b/lineage/tests/test_LineageTree.py
@@ -2,7 +2,7 @@
 import unittest
 import numpy as np
 from ..CellVar import CellVar as c
-from ..LineageTree import LineageTree, max_gen, get_leaves_idx
+from ..LineageTree import LineageTree, max_gen
 from ..states.StateDistributionGamma import StateDistribution
 
 
@@ -125,14 +125,3 @@ def test_get_parent_for_level(self):
         list_by_gen = max_gen(self.lineage1.output_lineage)
         parent_ind_holder = np.unique(self.lineage1.cell_to_parent[list_by_gen[3]])
         np.testing.assert_array_equal(parent_ind_holder, list_by_gen[2])
-
-    def test_get_leaves(self):
-        """
-        A unittest fot get_leaves function.
-        """
-        # getting the leaves and their indexes for lineage1
-        leaf_index = get_leaves_idx(self.lineage1.output_lineage)
-
-        # to check the indexes for leaf cells are true
-        for i in leaf_index:
-            self.assertTrue(self.lineage1.output_lineage[i].isLeaf())