diff --git a/python_modules/dagster/dagster/_core/asset_graph_view/asset_graph_view.py b/python_modules/dagster/dagster/_core/asset_graph_view/asset_graph_view.py
index f4860f3992071..56d2aa7398b30 100644
--- a/python_modules/dagster/dagster/_core/asset_graph_view/asset_graph_view.py
+++ b/python_modules/dagster/dagster/_core/asset_graph_view/asset_graph_view.py
@@ -250,8 +250,6 @@ def compute_mapped_subset(
         from_partitions_def = self.asset_graph.get(from_key).partitions_def
         to_partitions_def = self.asset_graph.get(to_key).partitions_def
 
-        partition_mapping = self.asset_graph.get_partition_mapping(from_key, to_key)
-
         if direction == "down":
             if from_partitions_def is None or to_partitions_def is None:
                 return (
@@ -259,6 +257,11 @@ def compute_mapped_subset(
                     if from_subset.is_empty
                     else self.get_full_subset(key=to_key)
                 )
+
+            child_key = to_key
+            parent_key = from_key
+            partition_mapping = self.asset_graph.get_partition_mapping(child_key, parent_key)
+
             to_partitions_subset = partition_mapping.get_downstream_partitions_for_partitions(
                 upstream_partitions_subset=from_subset.get_internal_subset_value(),
                 upstream_partitions_def=from_partitions_def,
@@ -273,6 +276,11 @@ def compute_mapped_subset(
                     if from_subset.is_empty
                     else self.get_full_subset(key=to_key)
                 )
+
+            child_key = from_key
+            parent_key = to_key
+            partition_mapping = self.asset_graph.get_partition_mapping(child_key, parent_key)
+
             to_partitions_subset = (
                 partition_mapping.get_upstream_mapped_partitions_result_for_partitions(
                     downstream_partitions_subset=from_subset.get_internal_subset_value()
diff --git a/python_modules/dagster/dagster_tests/asset_defs_tests/asset_graph_view_tests/test_basic_asset_graph_view.py b/python_modules/dagster/dagster_tests/asset_defs_tests/asset_graph_view_tests/test_basic_asset_graph_view.py
index dc5827e81f621..43696c2141fd6 100644
--- a/python_modules/dagster/dagster_tests/asset_defs_tests/asset_graph_view_tests/test_basic_asset_graph_view.py
+++ b/python_modules/dagster/dagster_tests/asset_defs_tests/asset_graph_view_tests/test_basic_asset_graph_view.py
@@ -62,12 +62,11 @@ def down_letters(): ...
     # from full up to down
     up_subset = asset_graph_view_t0.get_full_subset(key=up_numbers.key)
     assert up_subset.expensively_compute_partition_keys() == {"1", "2", "3"}
-    assert (
-        up_subset.compute_child_subset(down_letters.key).expensively_compute_partition_keys()
-        == set()
-    )
+    assert up_subset.compute_child_subset(
+        down_letters.key
+    ).expensively_compute_partition_keys() == {"a", "b", "c"}
 
-    # from full up to down
+    # from full down to up
     down_subset = asset_graph_view_t0.get_full_subset(key=down_letters.key)
     assert down_subset.expensively_compute_partition_keys() == {"a", "b", "c"}
     assert down_subset.compute_parent_subset(
@@ -98,12 +97,9 @@ def down_letters(): ...
     )
 
     # subset of up to subset of down
-    assert (
-        up_subset.compute_intersection_with_partition_keys({"2"})
-        .compute_child_subset(down_letters.key)
-        .expensively_compute_partition_keys()
-        == set()
-    )
+    assert up_subset.compute_intersection_with_partition_keys({"2"}).compute_child_subset(
+        down_letters.key
+    ).expensively_compute_partition_keys() == {"b"}
 
     # subset of down to subset of up
     assert down_subset.compute_intersection_with_partition_keys({"b"}).compute_parent_subset(