diff --git a/backends/functional/cxx_runtime/sim.h b/backends/functional/cxx_runtime/sim.h
index 040c6aefc..950d4c5e1 100644
--- a/backends/functional/cxx_runtime/sim.h
+++ b/backends/functional/cxx_runtime/sim.h
@@ -24,6 +24,7 @@
 #include <cassert>
 #include <string>
 #include <iostream>
+#include <algorithm>
 
 template<size_t n>
 class Signal {