diff --git a/configure.in b/configure.in
index 023ede7080..0df95deaf3 100644
--- a/configure.in
+++ b/configure.in
@@ -902,20 +902,25 @@ RUBY_INSTALL_NAME="${ri_prefix}ruby${ri_suffix}"
 case "$target_os" in
   cygwin*|mingw*|*djgpp*)
     RUBY_LIB_PREFIX="/lib/ruby"
-    SITEDIR='/lib/ruby/site_ruby'
     ;;
   *)
     RUBY_LIB_PREFIX="${prefix}/lib/ruby"
-    SITEDIR='${prefix}/lib/ruby/site_ruby'
     ;;
 esac
 RUBY_LIB_PATH="${RUBY_LIB_PREFIX}/${MAJOR}.${MINOR}"
-sitedir='${prefix}/lib/ruby/site_ruby'
+
 AC_ARG_WITH(sitedir,
 	    [--with-sitedir=DIR        site libraries in DIR [PREFIX/lib/ruby/site_ruby]],
             [sitedir=$withval],
-            [sitedir=`eval "echo ${SITEDIR}"`])
-RUBY_SITE_LIB_PATH="${sitedir}"
+            [sitedir='${prefix}/lib/ruby/site_ruby'])
+SITE_DIR="`eval "echo ${sitedir}"`"
+case "$target_os" in
+  cygwin*|mingw*|*djgpp*)
+    RUBY_SITE_LIB_PATH="`expr "$SITE_DIR" : "$prefix\(/.*\)"`" ||
+    RUBY_SITE_LIB_PATH="$SITE_DIR";;
+  *)
+    RUBY_SITE_LIB_PATH="$SITE_DIR";;
+esac
 RUBY_SITE_LIB_PATH2="${RUBY_SITE_LIB_PATH}/${MAJOR}.${MINOR}"
 
 AC_DEFINE_UNQUOTED(RUBY_LIB, "${RUBY_LIB_PATH}")