https://bugs.gentoo.org/429292
 
 src/basic_socket.cc | 1 +
 1 file changed, 1 insertion(+)

--- a/src/basic_socket.cc
+++ b/src/basic_socket.cc
@@ -22,6 +22,7 @@
  * @doctodo
  */
 
+#include <unistd.h>
 #include <socketstream/basic_socket.h>
 
 namespace ss {