diff --git a/openbox/debug.c b/openbox/debug.c
index 5a976d0c..42644868 100644
--- a/openbox/debug.c
+++ b/openbox/debug.c
@@ -26,6 +26,10 @@
 #include <stdio.h>
 #include <errno.h>
 
+#ifdef HAVE_UNISTD_H
+#  include <unistd.h>
+#endif
+
 static gboolean  enabled_types[OB_DEBUG_TYPE_NUM] = {FALSE};
 static FILE     *log_file = NULL;
 static guint     rr_handler_id = 0;