diff --git a/numba_rvsdg/core/datastructures/scfg.py b/numba_rvsdg/core/datastructures/scfg.py
index 3e3a96d..5018266 100644
--- a/numba_rvsdg/core/datastructures/scfg.py
+++ b/numba_rvsdg/core/datastructures/scfg.py
@@ -524,6 +524,11 @@ def insert_block(
         block_type: SyntheticBlock
             The type/class of the newly created block.
         """
+        # To prevent spurious mutations in successsors and predecessors
+        # since they are a part of the graph.
+        successors = successors.copy()
+        predecessors = predecessors.copy()
+
         # TODO: needs a diagram and documentaion
         # initialize new block
         new_block = block_type(