diff --git a/external/bsd/mdocml/Makefile.inc b/external/bsd/mdocml/Makefile.inc
index 293136f3c..242aa02a1 100644
--- a/external/bsd/mdocml/Makefile.inc
+++ b/external/bsd/mdocml/Makefile.inc
@@ -5,7 +5,7 @@
 VERSION!=	cd ${.PARSEDIR}/dist && ${MAKE} -V VERSION
 
 CPPFLAGS+=	-DVERSION=\"${VERSION}\" -DUGLY
-CPPFLAGS+=	-DOSNAME=\"Minix\"
+CPPFLAGS+=	-UOSNAME -DOSNAME=\"Minix\"
 
 .if (${HOSTPROG:U} == "")
 CPPFLAGS+=	-DHAVE_STRLCAT -DHAVE_STRLCPY -DHAVE_STRPTIME -DHAVE_MMAP
diff --git a/external/bsd/mdocml/dist/Makefile b/external/bsd/mdocml/dist/Makefile
index 934d6072f..87d9e5ca1 100644
--- a/external/bsd/mdocml/dist/Makefile
+++ b/external/bsd/mdocml/dist/Makefile
@@ -28,7 +28,7 @@ CFLAGS    += -g $(WFLAGS) $(VFLAGS) -DHAVE_CONFIG_H
 # Specify this if you want to hard-code the operating system to appear
 # in the lower-left hand corner of -mdoc manuals.
 # CFLAGS += -DOSNAME="\"OpenBSD 4.5\""
- CFLAGS += -DOSNAME="\"Minix\""
+CFLAGS += -UOSNAME -DOSNAME="\"Minix\""
 
 LINTFLAGS += $(VFLAGS)