diff --git a/be/src/exec/blocking-join-node.cc b/be/src/exec/blocking-join-node.cc
index 0f7676164..69fca7023 100644
--- a/be/src/exec/blocking-join-node.cc
+++ b/be/src/exec/blocking-join-node.cc
@@ -184,6 +184,15 @@ Status BlockingJoinNode::Open(RuntimeState* state) {
     // are fully constructed.
     RETURN_IF_ERROR(build_side_status.Get());
     RETURN_IF_ERROR(open_status);
+  } else if (IsInSubplan()) {
+    // When inside a subplan, open the first child before doing the build such that
+    // UnnestNodes on the probe side are opened and project their unnested collection
+    // slots. Otherwise, the build might unnecessarily deep-copy those collection slots,
+    // and this node would return them in GetNext().
+    // TODO: Remove this special-case behavior for subplans once we have proper
+    // projection. See UnnestNode for details on the current projection implementation.
+    RETURN_IF_ERROR(child(0)->Open(state));
+    RETURN_IF_ERROR(ConstructBuildSide(state));
   } else {
     RETURN_IF_ERROR(ConstructBuildSide(state));
     RETURN_IF_ERROR(child(0)->Open(state));
diff --git a/testdata/workloads/functional-query/queries/QueryTest/nested-types-runtime.test b/testdata/workloads/functional-query/queries/QueryTest/nested-types-runtime.test
index 0ce4f6730..fc7032484 100644
--- a/testdata/workloads/functional-query/queries/QueryTest/nested-types-runtime.test
+++ b/testdata/workloads/functional-query/queries/QueryTest/nested-types-runtime.test
@@ -375,3 +375,25 @@ where c_custkey < 10
 ---- TYPES
 BIGINT,BIGINT,BIGINT,INT,BIGINT
 ====
+---- QUERY
+# IMPALA-2456: Test subplan that contains a hash join with unnest nodes on both the build
+# and probe sides of the join. Tests projection of collection-typed slots on both sides
+# of the join.
+select c_custkey, o_orderkey
+from tpch_nested_parquet.customer c
+inner join c.c_orders o1
+left anti join
+  (select o2.o_orderkey x
+   from c.c_orders o2, c.c_orders o3) v
+on c.c_custkey = v.x
+where c_custkey < 2
+---- RESULTS
+1,454791
+1,579908
+1,3868359
+1,4273923
+1,4808192
+1,5133509
+---- TYPES
+bigint,bigint
+====