2 files changed, 3 insertions, 2 deletions
diff --git a/src/mbgl/style/expression/compound_expression.cpp b/src/mbgl/style/expression/compound_expression.cpp
index cc1d58025b..34f0f5dea3 100644
--- a/src/mbgl/style/expression/compound_expression.cpp
+++ b/src/mbgl/style/expression/compound_expression.cpp
@@ -423,7 +423,8 @@ const auto& propertiesCompoundExpression() {
             };
         }
         std::unordered_map<std::string, Value> result;
-        const PropertyMap properties = params.feature->getProperties();
+        const PropertyMap& properties = params.feature->getProperties();
+        result.reserve(properties.size());
         for (const auto& entry : properties) {
             result[entry.first] = toExpressionValue(entry.second);
         }
diff --git a/src/mbgl/style/expression/expression.cpp b/src/mbgl/style/expression/expression.cpp
index 4c810431d0..d61f435eec 100644
--- a/src/mbgl/style/expression/expression.cpp
+++ b/src/mbgl/style/expression/expression.cpp
@@ -15,7 +15,7 @@ public:
     FeatureType getType() const override  {
         return apply_visitor(ToFeatureType(), feature.geometry);
     }
-    PropertyMap getProperties() const override { return feature.properties; }
+    const PropertyMap& getProperties() const override { return feature.properties; }
     FeatureIdentifier getID() const override { return feature.id; }
     optional<mbgl::Value> getValue(const std::string& key) const override {
         auto it = feature.properties.find(key);