diff --git a/loki/transform/transform_parametrise.py b/loki/transform/transform_parametrise.py
index 78295f9ca..19907ca75 100644
--- a/loki/transform/transform_parametrise.py
+++ b/loki/transform/transform_parametrise.py
@@ -84,7 +84,7 @@
 from loki.expression import symbols as sym
 from loki import ir
 from loki.visitors import Transformer, FindNodes
-from loki.tools.util import is_iterable, as_tuple
+from loki.tools.util import as_tuple, CaseInsensitiveDict
 from loki.transform.transformation import Transformation
 from loki.transform.transform_inline import inline_constant_parameters
 
@@ -121,7 +121,7 @@ def error_stop(**kwargs):
 
         dic2p = {'a': 12, 'b': 11}
 
-        transformation = ParametriseTransformation(dic2p=dic2p, abort_callback=error_stop, 
+        transformation = ParametriseTransformation(dic2p=dic2p, abort_callback=error_stop,
                                 entry_points=("driver1", "driver2"))
 
         scheduler.process(transformation=transformation)
@@ -153,12 +153,7 @@ def error_stop(**kwargs):
     def __init__(self, dic2p, replace_by_value=False, entry_points=None, abort_callback=None, key=None):
         self.dic2p = dic2p
         self.replace_by_value = replace_by_value
-        if entry_points is not None:
-            self.entry_points = [_.upper() for _ in entry_points]
-        else:
-            self.entry_points = entry_points
-        if self.entry_points is not None:
-            assert is_iterable(entry_points)
+        self.entry_points = tuple(entry_point.upper() for entry_point in as_tuple(entry_points)) or None
         self.abort_callback = abort_callback
         if key is not None:
             self._key = key
@@ -181,9 +176,10 @@ def transform_subroutine(self, routine, **kwargs):
         item = kwargs.get('item', None)
         role = kwargs.get('role', None)
 
-        _successors = kwargs.get('successors', None)
-        successor_map = {successor.routine.name: successor for successor in _successors}
-        successors = [successor.local_name.upper() for successor in _successors]
+        successor_map = CaseInsensitiveDict(
+            (successor.local_name, successor)
+            for successor in as_tuple(kwargs.get('successors'))
+        )
 
         # decide whether subroutine is an entry point or not
         process_entry_point = False
@@ -248,7 +244,7 @@ def transform_subroutine(self, routine, **kwargs):
             # remove variables to be parametrised from all call statements
             call_map = {}
             for call in FindNodes(ir.CallStatement).visit(routine.body):
-                if str(call.name).upper() in successors:
+                if str(call.name) in successor_map:
                     successor_map[str(call.name)].trafo_data[self._key] = {}
                     arg_map = dict(call.arg_iter())
                     arg_map_reversed = {v: k for k, v in arg_map.items()}