Index: Makefile.in
==================================================================
--- Makefile.in
+++ Makefile.in
@@ -1,6 +1,6 @@
-prefix = UNSPECIFIED
+prefix = @prefix@
 exec_prefix = @exec_prefix@
 libdir = @libdir@
 
 TARGET = @TARGET@
 

Index: configure.ac
==================================================================
--- configure.ac
+++ configure.ac
@@ -1,7 +1,10 @@
 dnl Define ourselves
 AC_INIT(tcc4tcl, @@VERS@@)
+
+dnl Default prefix should be "UNSPECIFIED" to use magic in the Makefile
+ac_default_prefix="UNSPECIFIED"
 
 dnl Checks for programs.
 AC_PROG_CC
 AC_PROG_CPP
 AC_PROG_MAKE_SET