diff -Naur a/ocamldoc/Makefile.nt b/ocamldoc/Makefile.nt
--- a/ocamldoc/Makefile.nt	2010-05-28 12:21:46.000000000 +0100
+++ b/ocamldoc/Makefile.nt	2016-06-15 12:31:56.323953400 +0100
@@ -22,7 +22,7 @@
 OCAMLLIB = $(LIBDIR)
 OCAMLBIN = $(BINDIR)
 
-OCAMLPP=-pp "grep -v DEBUG"
+OCAMLPP=-pp "grep -va DEBUG"
 
 # For installation
 ##############