--- a/src/util/process.h
+++ b/src/util/process.h
@@ -35,6 +35,8 @@
 #include <memory>
 #include <string>
 
+#include <unistd.h>
+
 // forward declaration
 class Config;
 
--- a/src/util/process_executor.h
+++ b/src/util/process_executor.h
@@ -35,6 +35,8 @@
 #include <string>
 #include <vector>
 
+#include <unistd.h>
+
 #include "executor.h"
 
 class ProcessExecutor : public Executor {