1 files changed, 3 insertions, 2 deletions
diff --git a/src/mongo/db/pipeline/document_source_facet.cpp b/src/mongo/db/pipeline/document_source_facet.cpp
index ab927d4f228..c3085279e8f 100644
--- a/src/mongo/db/pipeline/document_source_facet.cpp
+++ b/src/mongo/db/pipeline/document_source_facet.cpp
@@ -208,10 +208,11 @@ Value DocumentSourceFacet::serialize(boost::optional<ExplainOptions::Verbosity>
     return Value(Document{{"$facet", serialized.freezeToValue()}});
 }
 
-void DocumentSourceFacet::addInvolvedCollections(vector<NamespaceString>* collections) const {
+void DocumentSourceFacet::addInvolvedCollections(
+    stdx::unordered_set<NamespaceString>* collectionNames) const {
     for (auto&& facet : _facets) {
         for (auto&& source : facet.pipeline->getSources()) {
-            source->addInvolvedCollections(collections);
+            source->addInvolvedCollections(collectionNames);
         }
     }
 }