diff --git a/wagtail/wagtailsearch/backends/elasticsearch5.py b/wagtail/wagtailsearch/backends/elasticsearch5.py
index 92e7be535..e3987124c 100644
--- a/wagtail/wagtailsearch/backends/elasticsearch5.py
+++ b/wagtail/wagtailsearch/backends/elasticsearch5.py
@@ -18,6 +18,27 @@ class Elasticsearch5Index(Elasticsearch2Index):
 class Elasticsearch5SearchQuery(Elasticsearch2SearchQuery):
     mapping_class = Elasticsearch5Mapping
 
+    def _process_lookup(self, field, lookup, value):
+        column_name = self.mapping.get_field_column_name(field)
+
+        if lookup == 'isnull':
+            query = {
+                'exists': {
+                    'field': column_name,
+                }
+            }
+
+            if value:
+                query = {
+                    'bool': {
+                        'mustNot': query
+                    }
+                }
+
+            return query
+
+        return super(Elasticsearch5SearchQuery, self)._process_lookup(field, lookup, value)
+
     def _connect_filters(self, filters, connector, negated):
         if filters:
             if len(filters) == 1:
diff --git a/wagtail/wagtailsearch/tests/test_elasticsearch5_backend.py b/wagtail/wagtailsearch/tests/test_elasticsearch5_backend.py
index 0e049b29d..bed0f88e3 100644
--- a/wagtail/wagtailsearch/tests/test_elasticsearch5_backend.py
+++ b/wagtail/wagtailsearch/tests/test_elasticsearch5_backend.py
@@ -410,7 +410,7 @@ class TestElasticsearch5SearchQuery(TestCase):
         # Check it
         expected_result = {'bool': {'filter': [
             {'match': {'content_type': 'searchtests.SearchTest'}},
-            {'missing': {'field': 'title_filter'}}
+            {'bool': {'mustNot': {'exists': {'field': 'title_filter'}}}}
         ], 'must': {'multi_match': {'query': 'Hello', 'fields': ['_all', '_partials']}}}}
         self.assertDictEqual(query.get_query(), expected_result)
 
@@ -421,7 +421,7 @@ class TestElasticsearch5SearchQuery(TestCase):
         # Check it
         expected_result = {'bool': {'filter': [
             {'match': {'content_type': 'searchtests.SearchTest'}},
-            {'missing': {'field': 'title_filter'}}
+            {'bool': {'mustNot': {'exists': {'field': 'title_filter'}}}}
         ], 'must': {'multi_match': {'query': 'Hello', 'fields': ['_all', '_partials']}}}}
         self.assertDictEqual(query.get_query(), expected_result)