diff --git a/amber/src/main/python/core/architecture/sendsemantics/hash_based_shuffle_partitioner.py b/amber/src/main/python/core/architecture/sendsemantics/hash_based_shuffle_partitioner.py
index de018e5a3ce..ceee764c1b8 100644
--- a/amber/src/main/python/core/architecture/sendsemantics/hash_based_shuffle_partitioner.py
+++ b/amber/src/main/python/core/architecture/sendsemantics/hash_based_shuffle_partitioner.py
@@ -37,18 +37,8 @@ def __init__(self, partitioning: HashBasedShufflePartitioning):
         super().__init__(set_one_of(Partitioning, partitioning))
         logger.debug(f"got {partitioning}")
         self.batch_size = partitioning.batch_size
-        # Partitioning contains an ordered list of downstream worker ids.
-        # Currently we are using the index of such an order to choose
-        # a downstream worker to send tuples to.
-        # Must use dict.fromkeys to ensure the order of receiver workers
-        # from partitioning is preserved (using `{}` to create a set
-        # does not preserve order and will not work correctly.)
-        self.receivers = [
-            (rid, [])
-            for rid in dict.fromkeys(
-                channel.to_worker_id for channel in partitioning.channels
-            )
-        ]
+        # Indexed by hash_code to choose the downstream worker to send to.
+        self.receivers = self.build_receiver_batches(partitioning.channels)
         self.hash_attribute_names = partitioning.hash_attribute_names
 
     @overrides
diff --git a/amber/src/main/python/core/architecture/sendsemantics/partitioner.py b/amber/src/main/python/core/architecture/sendsemantics/partitioner.py
index c4aac57cbe4..ed2332d5cba 100644
--- a/amber/src/main/python/core/architecture/sendsemantics/partitioner.py
+++ b/amber/src/main/python/core/architecture/sendsemantics/partitioner.py
@@ -32,6 +32,18 @@ class Partitioner(ABC):
     def __init__(self, partitioning: Message):
         self.partitioning: Partitioning = get_one_of(partitioning)
 
+    @staticmethod
+    def build_receiver_batches(
+        channels,
+    ) -> typing.List[typing.Tuple[ActorVirtualIdentity, typing.List[Tuple]]]:
+        # An ordered (receiver, batch) pair per distinct downstream worker.
+        # dict.fromkeys preserves the channel order; a set literal would not,
+        # which breaks input-port materialization reader threads.
+        return [
+            (rid, [])
+            for rid in dict.fromkeys(channel.to_worker_id for channel in channels)
+        ]
+
     def add_tuple_to_batch(
         self, tuple_: Tuple
     ) -> Iterator[typing.Tuple[ActorVirtualIdentity, typing.List[Tuple]]]:
diff --git a/amber/src/main/python/core/architecture/sendsemantics/range_based_shuffle_partitioner.py b/amber/src/main/python/core/architecture/sendsemantics/range_based_shuffle_partitioner.py
index 28aff35935f..3f8f83c504b 100644
--- a/amber/src/main/python/core/architecture/sendsemantics/range_based_shuffle_partitioner.py
+++ b/amber/src/main/python/core/architecture/sendsemantics/range_based_shuffle_partitioner.py
@@ -37,18 +37,8 @@ def __init__(self, partitioning: RangeBasedShufflePartitioning):
         super().__init__(set_one_of(Partitioning, partitioning))
         logger.info(f"got {partitioning}")
         self.batch_size = partitioning.batch_size
-        # Partitioning contains an ordered list of downstream worker ids.
-        # Currently we are using the index of such an order to choose
-        # a downstream worker to send tuples to.
-        # Must use dict.fromkeys to ensure the order of receiver workers
-        # from partitioning is preserved (using `{}` to create a set
-        # does not preserve order and will not work correctly.)
-        self.receivers = [
-            (rid, [])
-            for rid in dict.fromkeys(
-                channel.to_worker_id for channel in partitioning.channels
-            )
-        ]
+        # Indexed by get_receiver_index to choose the downstream worker to send to.
+        self.receivers = self.build_receiver_batches(partitioning.channels)
         self.range_attribute_names = partitioning.range_attribute_names
         self.range_min = partitioning.range_min
         self.range_max = partitioning.range_max
diff --git a/amber/src/main/python/core/architecture/sendsemantics/round_robin_partitioner.py b/amber/src/main/python/core/architecture/sendsemantics/round_robin_partitioner.py
index 87c3fee87d8..21c1a3ca0f4 100644
--- a/amber/src/main/python/core/architecture/sendsemantics/round_robin_partitioner.py
+++ b/amber/src/main/python/core/architecture/sendsemantics/round_robin_partitioner.py
@@ -35,19 +35,8 @@ class RoundRobinPartitioner(Partitioner):
     def __init__(self, partitioning: RoundRobinPartitioning):
         super().__init__(set_one_of(Partitioning, partitioning))
         self.batch_size = partitioning.batch_size
-        # Partitioning contains an ordered list of downstream worker ids.
-        # Currently we are using the index of such an order to choose
-        # a downstream worker to send tuples to.
-        # Must use dict.fromkeys to ensure the order of receiver workers
-        # from partitioning is preserved (using `{}` to create a set
-        # does not preserve order and will not work with input-port
-        # materialization reader threads.)
-        self.receivers = [
-            (rid, [])
-            for rid in dict.fromkeys(
-                channel.to_worker_id for channel in partitioning.channels
-            )
-        ]
+        # Indexed by round_robin_index to choose the downstream worker to send to.
+        self.receivers = self.build_receiver_batches(partitioning.channels)
         self.round_robin_index = 0
 
     @overrides