diff --git a/Documentation/Makefile b/Documentation/Makefile
index bb21d6af44..3cfa360a9e 100644
--- a/Documentation/Makefile
+++ b/Documentation/Makefile
@@ -17,14 +17,14 @@ DOC_HTML += $(patsubst %,%.html,$(ARTICLES) $(SP_ARTICLES))
 DOC_MAN1=$(patsubst %.txt,%.1,$(MAN1_TXT))
 DOC_MAN7=$(patsubst %.txt,%.7,$(MAN7_TXT))
 
-prefix=$(HOME)
+prefix?=$(HOME)
 bin=$(prefix)/bin
 mandir=$(prefix)/man
 man1=$(mandir)/man1
 man7=$(mandir)/man7
 # DESTDIR=
 
-INSTALL=install
+INSTALL?=install
 
 #
 # Please note that there is a minor bug in asciidoc.
diff --git a/Makefile b/Makefile
index 7ca77cf2af..bcda943273 100644
--- a/Makefile
+++ b/Makefile
@@ -293,7 +293,7 @@ SCRIPTS = $(patsubst %.sh,%,$(SCRIPT_SH)) \
 	  $(patsubst %.py,%,$(SCRIPT_PYTHON)) \
 	  gitk
 
-export TAR INSTALL DESTDIR SHELL_PATH
+export prefix TAR INSTALL DESTDIR SHELL_PATH
 ### Build rules
 
 all: $(PROGRAMS) $(SCRIPTS)