diff --git a/x-pack/plugins/apm/server/lib/ui_filters/local_ui_filters/get_local_filter_query.ts b/x-pack/plugins/apm/server/lib/ui_filters/local_ui_filters/get_local_filter_query.ts
index d8d6f9214f742..cfbd79d37c041 100644
--- a/x-pack/plugins/apm/server/lib/ui_filters/local_ui_filters/get_local_filter_query.ts
+++ b/x-pack/plugins/apm/server/lib/ui_filters/local_ui_filters/get_local_filter_query.ts
@@ -23,17 +23,15 @@ export const getLocalFilterQuery = ({
   const field = localUIFilters[localUIFilterName];
   const filter = getUiFiltersES(omit(uiFilters, field.name));
 
-  const projectionSource =
-    projection.body.aggs &&
-    projection.body.aggs[Object.keys(projection.body.aggs)[0]].terms;
-  const bucketCountAggregation = projectionSource
+  const bucketCountAggregation = projection.body.aggs
     ? {
         aggs: {
           bucket_count: {
-            cardinality:
-              'field' in projectionSource
-                ? { field: projectionSource.field }
-                : { script: projectionSource.script },
+            cardinality: {
+              field:
+                projection.body.aggs[Object.keys(projection.body.aggs)[0]].terms
+                  .field,
+            },
           },
         },
       }
diff --git a/x-pack/plugins/apm/server/projections/typings.ts b/x-pack/plugins/apm/server/projections/typings.ts
index 77a5beaf54605..332ac533e78c6 100644
--- a/x-pack/plugins/apm/server/projections/typings.ts
+++ b/x-pack/plugins/apm/server/projections/typings.ts
@@ -15,7 +15,7 @@ export type Projection = Omit<APMEventESSearchRequest, 'body'> & {
   body: Omit<ESSearchBody, 'aggs'> & {
     aggs?: {
       [key: string]: {
-        terms: AggregationOptionsByType['terms'];
+        terms: AggregationOptionsByType['terms'] & { field: string };
         aggs?: AggregationInputMap;
       };
     };