diff --git a/Makefile.in b/Makefile.in
index ee92e6e5..6c18318a 100644
--- a/Makefile.in
+++ b/Makefile.in
@@ -50,7 +50,7 @@ endif
 
 # Installation directories
 
-prefix       := @prefix@
+prefix       ?= @prefix@
 
 INSTALLDIR ?= $(DESTDIR)$(prefix)