diff --git a/libguile/iselect.c b/libguile/iselect.c
index 46ef923e7..ea0be94f0 100644
--- a/libguile/iselect.c
+++ b/libguile/iselect.c
@@ -43,6 +43,10 @@
 #include <limits.h>
 #include <string.h>
 
+#ifdef HAVE_UNISTD_H
+#include <unistd.h>
+#endif
+
 #include "libguile/_scm.h"
 #include "libguile/async.h"