diff --git a/common-rules.mk b/common-rules.mk
index 812bd62dbaf3e90574c80070636324a0f2f8ee0f..8dd72434a4f66819c377954315fbead9240e6b60 100644
--- a/common-rules.mk
+++ b/common-rules.mk
@@ -17,7 +17,7 @@
 
 CLEANFILES = *~ *.cmi *.cmo *.cmx *.cma *.cmxa *.o
 
-OCAMLCFLAGS = -g -warn-error CDEFLMPSUVYZX
+OCAMLCFLAGS = -g -warn-error CDEFLMPSUVYZX-3
 OCAMLCPACKAGES = -package unix,calendar -I $(top_builddir)
 OCAMLOPTFLAGS = $(OCAMLCFLAGS)
 OCAMLOPTPACKAGES = $(OCAMLCPACKAGES)