diff --git a/test/test_protocol.cxx b/test/test_protocol.cxx
index d7ea7cd87..e80e4fe6d 100644
--- a/test/test_protocol.cxx
+++ b/test/test_protocol.cxx
@@ -8,6 +8,8 @@
 #include <cppunit/ui/text/TestRunner.h>
 #include <cppunit/extensions/HelperMacros.h>
 
+#include <unistd.h>
+
 static enum ack last_error = ack(-1);
 
 void