diff --git a/include/libsigrok/proto.h b/include/libsigrok/proto.h
index c10f7c10..ea9d4779 100644
--- a/include/libsigrok/proto.h
+++ b/include/libsigrok/proto.h
@@ -20,6 +20,8 @@
 #ifndef LIBSIGROK_PROTO_H
 #define LIBSIGROK_PROTO_H
 
+#include <unistd.h>
+
 /**
  * @file
  *