diff --git a/cde/lib/DtHelp/Obsolete.c b/cde/lib/DtHelp/Obsolete.c
index 398cd8874..61eac0382 100644
--- a/cde/lib/DtHelp/Obsolete.c
+++ b/cde/lib/DtHelp/Obsolete.c
@@ -48,6 +48,7 @@
  * system includes
  */
 #include <stdlib.h>
+#include <unistd.h>
 
 /*
  * Canvas Engine