diff --git a/google-cloud-datastore/src/main/java/com/google/cloud/datastore/execution/request/AggregationQueryRequestProtoPreparer.java b/google-cloud-datastore/src/main/java/com/google/cloud/datastore/execution/request/AggregationQueryRequestProtoPreparer.java
index b5da8d9fe..8f4e51d6e 100644
--- a/google-cloud-datastore/src/main/java/com/google/cloud/datastore/execution/request/AggregationQueryRequestProtoPreparer.java
+++ b/google-cloud-datastore/src/main/java/com/google/cloud/datastore/execution/request/AggregationQueryRequestProtoPreparer.java
@@ -26,6 +26,7 @@
 import com.google.cloud.datastore.ReadOptionProtoPreparer;
 import com.google.cloud.datastore.StructuredQueryProtoPreparer;
 import com.google.cloud.datastore.aggregation.Aggregation;
+import com.google.common.base.MoreObjects;
 import com.google.datastore.v1.GqlQuery;
 import com.google.datastore.v1.PartitionId;
 import com.google.datastore.v1.Query;
@@ -92,9 +93,9 @@ private com.google.datastore.v1.AggregationQuery getAggregationQuery(
   private PartitionId getPartitionId(AggregationQuery aggregationQuery) {
     PartitionId.Builder builder =
         PartitionId.newBuilder().setProjectId(datastoreOptions.getProjectId());
-    if (aggregationQuery.getNamespace() != null) {
-      builder.setNamespaceId(aggregationQuery.getNamespace());
-    }
+    String namespace =
+        MoreObjects.firstNonNull(aggregationQuery.getNamespace(), datastoreOptions.getNamespace());
+    builder.setNamespaceId(namespace);
     return builder.build();
   }
 }
diff --git a/google-cloud-datastore/src/test/java/com/google/cloud/datastore/execution/request/AggregationQueryRequestProtoPreparerTest.java b/google-cloud-datastore/src/test/java/com/google/cloud/datastore/execution/request/AggregationQueryRequestProtoPreparerTest.java
index 6301ebeff..934e3a4c7 100644
--- a/google-cloud-datastore/src/test/java/com/google/cloud/datastore/execution/request/AggregationQueryRequestProtoPreparerTest.java
+++ b/google-cloud-datastore/src/test/java/com/google/cloud/datastore/execution/request/AggregationQueryRequestProtoPreparerTest.java
@@ -154,7 +154,7 @@ public void shouldPrepareReadOptionsWithGivenGqlQuery() {
   }
 
   @Test
-  public void shouldPrepareAggregationQueryWithoutNamespace() {
+  public void shouldPrepareAggregationQueryWithNamespaceFromDatastoreOptions() {
     AggregationQuery structuredQueryWithoutNamespace =
         Query.newAggregationQueryBuilder()
             .addAggregation(count().as("total"))
@@ -169,8 +169,9 @@ public void shouldPrepareAggregationQueryWithoutNamespace() {
         protoPreparer.prepare(QueryAndReadOptions.create(gqlQueryWithoutNamespace));
 
     assertThat(runAggregationQueryFromStructuredQuery.getPartitionId().getNamespaceId())
-        .isEqualTo("");
-    assertThat(runAggregationQueryFromGqlQuery.getPartitionId().getNamespaceId()).isEqualTo("");
+        .isEqualTo(NAMESPACE);
+    assertThat(runAggregationQueryFromGqlQuery.getPartitionId().getNamespaceId())
+        .isEqualTo(NAMESPACE);
   }
 
   private RunAggregationQueryRequest prepareQuery(AggregationQuery query, ReadOption readOption) {