diff --git a/frontends/concrete-python/examples/levenshtein_distance/levenshtein_distance.py b/frontends/concrete-python/examples/levenshtein_distance/levenshtein_distance.py
index 04382dd3d1..cf65cf6ec8 100644
--- a/frontends/concrete-python/examples/levenshtein_distance/levenshtein_distance.py
+++ b/frontends/concrete-python/examples/levenshtein_distance/levenshtein_distance.py
@@ -40,6 +40,7 @@ def dna():
 
     def __init__(self, letters: str):
         self.letters = letters
+        self.mapping_to_int = {}
 
         for i, c in enumerate(self.letters):
             self.mapping_to_int[c] = i
@@ -75,7 +76,10 @@ def random_pick_in_values(self) -> int:
 
     def _random_string(self, length: int) -> str:
         """Pick a random string in the alphabet."""
-        return "".join([random.choice(list(self.mapping_to_int)) for _ in range(length)])
+        ans = "".join([random.choice(list(self.mapping_to_int)) for _ in range(length)])
+        check = [c in self.letters for c in ans]
+        assert all(check), "Issue in generation"
+        return ans
 
     def prepare_random_patterns(self, len_min: int, len_max: int, nb_strings: int) -> list:
         """Prepare random patterns of different lengths."""
@@ -223,18 +227,15 @@ def _compute_in_fhe(self, list_patterns: list, show_distance: bool = False):
 # Module FHE
 @fhe.module()
 class LevenshsteinModule:
-    @staticmethod
     @fhe.function({"x": "encrypted", "y": "encrypted"})
     def equal(x, y):
         """Assert equality between two chars of the alphabet."""
         return x == y
 
-    @staticmethod
     @fhe.function({"x": "clear"})
     def constant(x):
         return fhe.zero() + x
 
-    @staticmethod
     @fhe.function(
         {
             "is_equal": "encrypted",