diff --git a/include/cosim/timer.hpp b/include/cosim/timer.hpp
index c51b8638..1fad5c2c 100644
--- a/include/cosim/timer.hpp
+++ b/include/cosim/timer.hpp
@@ -15,7 +15,6 @@
 
 #include <atomic>
 #include <memory>
-#include <mutex>
 
 namespace cosim
 {