Keep gcc -Wall happy.
diff --git a/Modules/signalmodule.c b/Modules/signalmodule.c
index 48eb03d..9e7f239 100644
--- a/Modules/signalmodule.c
+++ b/Modules/signalmodule.c
@@ -34,6 +34,10 @@
 #include "Python.h"
 #include "intrcheck.h"
 
+#ifdef HAVE_UNISTD_H
+#include <unistd.h>
+#endif
+
 #include <signal.h>
 
 #ifndef SIG_ERR