diff --git a/src/sys2.h b/src/sys2.h
index 608307216..a68327e18 100644
--- a/src/sys2.h
+++ b/src/sys2.h
@@ -1,3 +1,8 @@
+/* WARNING -- this file is temporary.  It is shared between the
+   sh-utils, fileutils, and textutils packages.  Once I find a little
+   more time, I'll merge the remaining things in system.h and everything
+   in this file will go back there. */
+
 #ifndef RETSIGTYPE
 # define RETSIGTYPE void
 #endif