diff --git a/dartsim/src/EntityManagementFeatures.cc b/dartsim/src/EntityManagementFeatures.cc
index 2ca9d27d0..69cc1ff77 100644
--- a/dartsim/src/EntityManagementFeatures.cc
+++ b/dartsim/src/EntityManagementFeatures.cc
@@ -19,6 +19,7 @@
 
 #include <memory>
 #include <string>
+#include <unordered_map>
 
 #include <dart/config.hpp>
 #include <dart/collision/ode/OdeCollisionDetector.hpp>