diff --git a/Makefile b/Makefile
index c1fdfd0cc6..811803c879 100644
--- a/Makefile
+++ b/Makefile
@@ -33,7 +33,7 @@ git-union-merge.1: doc/git-union-merge.mdwn
 git-union-merge:
 	$(GHC) --make -threaded $@
 
-SHAREDIR=share
+SHAREDIR?=share
 
 install-mans: $(mans)
 	install -d $(DESTDIR)$(PREFIX)/$(SHAREDIR)/man/man1