diff --git a/wagtail/search/backends/elasticsearch2.py b/wagtail/search/backends/elasticsearch2.py
index e61035c0c..c758c227f 100644
--- a/wagtail/search/backends/elasticsearch2.py
+++ b/wagtail/search/backends/elasticsearch2.py
@@ -4,7 +4,7 @@ from urllib.parse import urlparse
 
 from django.db import DEFAULT_DB_ALIAS, models
 from django.db.models.sql import Query
-from django.db.models.sql.constants import SINGLE
+from django.db.models.sql.constants import MULTI
 from django.utils.crypto import get_random_string
 from elasticsearch import Elasticsearch, NotFoundError
 from elasticsearch.helpers import bulk
@@ -340,8 +340,11 @@ class Elasticsearch2SearchQuery(BaseSearchQuery):
         if lookup == 'in':
             if isinstance(value, Query):
                 db_alias = self.queryset._db or DEFAULT_DB_ALIAS
-                value = (value.get_compiler(db_alias)
-                         .execute_sql(result_type=SINGLE))
+                value = next(value.get_compiler(db_alias)
+                                  .execute_sql(result_type=MULTI))
+
+                value = [r[0] for r in value]
+
             elif not isinstance(value, list):
                 value = list(value)
             return {
diff --git a/wagtail/search/tests/test_elasticsearch2_backend.py b/wagtail/search/tests/test_elasticsearch2_backend.py
index 8fd6989b7..1f2fd22da 100644
--- a/wagtail/search/tests/test_elasticsearch2_backend.py
+++ b/wagtail/search/tests/test_elasticsearch2_backend.py
@@ -19,11 +19,6 @@ from .test_backends import BackendTests
 class TestElasticsearch2SearchBackend(BackendTests, ElasticsearchCommonSearchBackendTests, TestCase):
     backend_path = 'wagtail.search.backends.elasticsearch2'
 
-    # Broken
-    @unittest.expectedFailure
-    def test_filter_in_values_list_subquery(self):
-        super(TestElasticsearch2SearchBackend, self).test_filter_in_values_list_subquery()
-
     # Broken
     @unittest.expectedFailure
     def test_order_by_non_filterable_field(self):
diff --git a/wagtail/search/tests/test_elasticsearch5_backend.py b/wagtail/search/tests/test_elasticsearch5_backend.py
index 4804d7818..513fc749c 100644
--- a/wagtail/search/tests/test_elasticsearch5_backend.py
+++ b/wagtail/search/tests/test_elasticsearch5_backend.py
@@ -23,11 +23,6 @@ class TestElasticsearch5SearchBackend(BackendTests, ElasticsearchCommonSearchBac
     def test_filter_isnull_true(self):
         super(TestElasticsearch5SearchBackend, self).test_filter_isnull_true()
 
-    # Broken
-    @unittest.expectedFailure
-    def test_filter_in_values_list_subquery(self):
-        super(TestElasticsearch5SearchBackend, self).test_filter_in_values_list_subquery()
-
     # Broken
     @unittest.expectedFailure
     def test_order_by_non_filterable_field(self):