diff --git a/src/keogram.cpp b/src/keogram.cpp
index c80ad1d0e..dc4152680 100644
--- a/src/keogram.cpp
+++ b/src/keogram.cpp
@@ -14,6 +14,7 @@ using namespace std;
 #include <sys/time.h>
 #include <cstdlib>
 #include <iostream>
+#include <mutex>
 #include <string>
 #include <thread>
 #include <vector>