diff --git a/src/hydra-queue-runner/dispatcher.cc b/src/hydra-queue-runner/dispatcher.cc
index 6d738ded..a4c84252 100644
--- a/src/hydra-queue-runner/dispatcher.cc
+++ b/src/hydra-queue-runner/dispatcher.cc
@@ -2,6 +2,7 @@
 #include <cmath>
 #include <thread>
 #include <unordered_map>
+#include <unordered_set>
 
 #include "state.hh"