diff --git a/src/concrete/ml/quantization/quantized_module_passes.py b/src/concrete/ml/quantization/quantized_module_passes.py
index 14ca0a5f8..c96c0edf4 100644
--- a/src/concrete/ml/quantization/quantized_module_passes.py
+++ b/src/concrete/ml/quantization/quantized_module_passes.py
@@ -1,5 +1,6 @@
 """Optimization passes for QuantizedModules."""
 from typing import Dict, List, Optional, Tuple
+from collections import defaultdict
 
 import numpy
 
@@ -59,6 +60,8 @@ def process(self) -> PatternDict:
         another Gemm/conv node. Optionally a Relu can be placed before this input
         quantization node.
 
+        Nothing will be done if rounding is already specified.
+
         Returns:
             result (PatternDict): a dictionary containing for each Conv/Gemm node for which
                 round PBS can be applied based on power-of-two scaling factors
@@ -92,7 +95,7 @@ def compute_op_predecessors(self) -> PredecessorsType:
         """
 
         # Initialize the list of predecessors with tensors that are graph inputs
-        predecessors: PredecessorsType = {}
+        predecessors: PredecessorsType = defaultdict(list)
 
         for (node_inputs, node_op) in self._qmodule.quant_layers_dict.values():
             # The first input node contains the encrypted data
@@ -105,10 +108,7 @@ def compute_op_predecessors(self) -> PredecessorsType:
             pred = self._qmodule.quant_layers_dict.get(enc_input_node, (None, None))
             # Get the quantized op that produces the current op's input
             pred_with_output = (pred[1], enc_input_node)
-            if node_op not in predecessors:
-                predecessors[node_op] = [pred_with_output]
-            else:
-                predecessors[node_op].append(pred_with_output)
+            predecessors[node_op].append(pred_with_output)
         return predecessors
 
     def match_path_pattern(
@@ -116,7 +116,7 @@ def match_path_pattern(
         predecessors: PredecessorsType,
         nodes_in_path: List[QuantizedOp],
         input_producer_of_path: Optional[QuantizedOp],
-    ):
+    ) -> bool:
         """Determine if a pattern has the structure that makes it viable for roundPBS.
 
         Args:
@@ -182,6 +182,8 @@ def detect_patterns(self, predecessors: PredecessorsType) -> PatternDict:
                         "Power of Two adapter: Error during graph traversal",
                     )
                     # If multiple ops produced this node, the pattern is not matched
+                    
+                    assert back_node is not None
                     if len(predecessors[back_node]) > 1:
                         break
 
@@ -192,6 +194,7 @@ def detect_patterns(self, predecessors: PredecessorsType) -> PatternDict:
                         # The Gemm/Conv op that produces this integer node is the one
                         # onto which we apply the roundPBS optimization
                         nodes_in_path.append(back_node)
+                        assert back_node is not None
                         list_pred_of_path = predecessors.get(back_node, None)
                         if list_pred_of_path is not None and len(list_pred_of_path) == 1:
                             integer_node_input_quant = list_pred_of_path[0][0]
@@ -227,7 +230,9 @@ def integer_log2(value: float) -> Tuple[int, bool]:
 
         invalid_paths: List[QuantizedMixingOp] = []
         for path_start_node, (path, path_input_quant) in valid_paths.items():
+            # Placeholders
             scale_input, scale_output, scale_weights = None, None, None
+            # Populate placeholders
             for node in path:
                 if isinstance(node, self.SUPPORTED_ROUND_PBS_OPS):
                     # Get the scale of the input of the Gemm/Conv node
@@ -241,6 +246,7 @@ def integer_log2(value: float) -> Tuple[int, bool]:
                     # node that will apply roundPBS
                     scale_output = node.constant_inputs[1]
 
+            # Check placeholders
             assert scale_input is not None, (
                 "Power of two adapter: Can not determine input scale of pattern",
             )
@@ -251,10 +257,12 @@ def integer_log2(value: float) -> Tuple[int, bool]:
                 "Power of two adapter: Can not determine output scale of pattern",
             )
 
+            # Check if power of two
             log2_input, ok_input = integer_log2(scale_input)
             log2_weights, ok_weights = integer_log2(scale_weights)
             log2_output, ok_output = integer_log2(scale_output)
 
+            # Modify rounding
             if ok_input and ok_weights and ok_output:
                 assert_true(
                     path_start_node.rounding_threshold_bits is None,