diff --git a/numba_rvsdg/core/datastructures/ast_transforms.py b/numba_rvsdg/core/datastructures/ast_transforms.py
index a51ba8d..410ae2b 100644
--- a/numba_rvsdg/core/datastructures/ast_transforms.py
+++ b/numba_rvsdg/core/datastructures/ast_transforms.py
@@ -787,7 +787,7 @@ def codegen_view() -> list[Any]:
             ]
         elif type(block) is SyntheticTail:
             # Synthetic tails do nothing.
-            pass
+            return []
         elif type(block) is SyntheticFill:
             # Synthetic fills must have a pass statement to main syntactical
             # correctness of the final program.
@@ -861,7 +861,8 @@ def if_cascade(jump_targets: list[str]) -> list[ast.AST]:
             return if_cascade(list(block.jump_targets[::-1]))
         else:
             raise NotImplementedError
-        return []
+
+        raise NotImplementedError("unreachable")
 
 
 def AST2SCFG(code: str | list[ast.FunctionDef] | Callable[..., Any]) -> SCFG: