diff --git a/sys/unix/Makefile.doc b/sys/unix/Makefile.doc
index dfb812700..5dbe117f0 100644
--- a/sys/unix/Makefile.doc
+++ b/sys/unix/Makefile.doc
@@ -12,6 +12,7 @@ NHSROOT=..
 MAKEDEFS = ../util/makedefs
 
 #STRIPBS ?= ../util/stripbs
+NROFF ?= nroff
 
 # Which version do we want to build?  (XXX These are not used anywhere.)
 GUIDEBOOK = Guidebook		# regular ASCII file
@@ -33,13 +34,13 @@ PSCMD ?= groff
 
 # Use the "cat" GUIDECMD if nroff and/or tbl and/or col are not installed
 # Not appropriate for creating Guidebook.txt.
-# GUIDECMD = cat Guidebook.txt
+# GUIDECMD ?= cat Guidebook.txt
 #
 # Single page. Might need adjustment to .pl value
-# GUIDECMD= $(GUIDE_PREFORMAT) | perl -pe 's/^(.mt)$$/.pl 4720v\n.in 0\n.po 8\n.ll 64m\n$$1/' | nroff -c -Tascii | $(COLCMD)
+# GUIDECMD= $(GUIDE_PREFORMAT) | perl -pe 's/^(.mt)$$/.pl 4720v\n.in 0\n.po 8\n.ll 64m\n$$1/' | $(NROFF) -c -Tascii | $(COLCMD)
 #
-GUIDECMD ?= $(GUIDE_PREFORMAT) | nroff -c -Tascii $(NROFF_FLAGS) | $(COLCMD)
-ONEPAGECMD ?= $(ONEPAGE_PREFORMAT) | nroff -c -Tascii $(NROFF_FLAGS) | $(COLCMD)
+GUIDECMD ?= $(GUIDE_PREFORMAT) | $(NROFF) -c -Tascii $(NROFF_FLAGS) | $(COLCMD)
+ONEPAGECMD ?= $(ONEPAGE_PREFORMAT) | $(NROFF) -c -Tascii $(NROFF_FLAGS) | $(COLCMD)
 
 # Only generate output for the current configuration:
 NHGREP = $(MAKEDEFS) --grep --input - --output -
@@ -51,14 +52,14 @@ NEEDMAKEDEFS = $(MAKEDEFS)
 #NHGREP = cat
 #NEEDMAKEDEFS =
 
-GUIDEBOOK_MN_SRC = Guidebook.mn
-GUIDEBOOK_MN = $(GUIDEBOOK_MN_SRC)
-GUIDEBOOK_TEX_SRC = Guidebook.tex
-GUIDEBOOK_TEX = $(GUIDEBOOK_TEX_SRC)
+GUIDEBOOK_MN_SRC ?= Guidebook.mn
+GUIDEBOOK_MN ?= $(GUIDEBOOK_MN_SRC)
+GUIDEBOOK_TEX_SRC ?= Guidebook.tex
+GUIDEBOOK_TEX ?= $(GUIDEBOOK_TEX_SRC)
 
-GUIDE_PREFORMAT = cat $(GUIDEBOOK_MN) | $(NHGREP) | tbl tmac.n -
+GUIDE_PREFORMAT ?= cat $(GUIDEBOOK_MN) | $(NHGREP) | tbl tmac.n -
 # for Guidebook.dat, unpaginated version of Guidebook.txt
-ONEPAGE_PREFORMAT = cat Gbk-1pg-pfx.mn $(GUIDEBOOK_MN) Gbk-1pg-sfx.mn \
+ONEPAGE_PREFORMAT ?= cat Gbk-1pg-pfx.mn $(GUIDEBOOK_MN) Gbk-1pg-sfx.mn \
 	| $(NHGREP) | tbl tmac.n -
 
 # the basic guidebook
@@ -91,7 +92,6 @@ $(MAKEDEFS)	: ../util/makedefs.c ../include/config.h ../src/mdlib.c \
 GAME	= nethack
 MANDIR	?= /usr/man/man6
 MANEXT	= 6
-NROFF ?= nroff
 
 # manual installation for most BSD-style systems
 GAMEMANCREATE = cat nethack.6 | $(NHGREP) >
@@ -99,10 +99,10 @@ RCVRMANCREATE = cat recover.6 | $(NHGREP) >
 DLBMANCREATE = cat dlb.6 | $(NHGREP) >
 MDMANCREATE = cat makedefs.6 | $(NHGREP) >
 # manual installation for most SYSV-style systems
-# GAMEMANCREATE = cat nethack.6 | $(NHGREP) | nroff -man - >
-# RCVRMANCREATE = cat recover.6 | $(NHGREP) | nroff -man - >
-# DLBMANCREATE = cat dlb.6 | $(NHGREP) | nroff -man - >
-# MDMANCREATE = cat makedefs.6 | $(NHGREP) | nroff -man - >
+# GAMEMANCREATE = cat nethack.6 | $(NHGREP) | $(NROFF) -man - >
+# RCVRMANCREATE = cat recover.6 | $(NHGREP) | $(NROFF) -man - >
+# DLBMANCREATE = cat dlb.6 | $(NHGREP) | $(NROFF) -man - >
+# MDMANCREATE = cat makedefs.6 | $(NHGREP) | $(NROFF) -man - >
 
 manpages: $(PREMANPAGES)
 	-$(GAMEMANCREATE) $(MANDIR)/$(GAME).$(MANEXT)