diff --git a/Makefile.in b/Makefile.in
index 4faabc3..3135f08 100644
--- a/Makefile.in
+++ b/Makefile.in
@@ -138,7 +138,8 @@ fake.rb:    Makefile
                  end; \
                end; \
                prehook = proc do |e|; \
-                 Config::MAKEFILE_CONFIG["top_srcdir"] = $$top_srcdir = "@top_srcdir@" unless e; \
+                 builddir = File.expand_path(File.dirname(__FILE__)); \
+                 Config::MAKEFILE_CONFIG["top_srcdir"] = $$top_srcdir = File.expand_path("@top_srcdir@", builddir) unle
                  untrace_var(:$$extmk, prehook); \
                end; \
                trace_var(:$$extmk, prehook); \