diff --git a/.gitignore b/.gitignore
index 94e6fe6d..24664d3a 100644
--- a/.gitignore
+++ b/.gitignore
@@ -16,4 +16,5 @@ build_dynamic/
 autom4te.cache/
 .openssl_build_done
 .openssl_configure_done
+.mruby_version
 .vagrant/
diff --git a/Makefile.in b/Makefile.in
index 2d782413..29dd8360 100644
--- a/Makefile.in
+++ b/Makefile.in
@@ -61,16 +61,27 @@ clean:
 	-rm -rf mrbgems_config mrbgems_config_dynamic
 
 clobber: clean_mruby clean
-	-rm -rf tmp autom4te.cache config config.status config.log $(BUILD_DIR) .openssl_build_done .openssl_configure_done
+	-rm -rf tmp autom4te.cache config config.status config.log $(BUILD_DIR) .openssl_build_done .openssl_configure_done .mruby_version
 
 #
 # mruby
 #
 build_mruby: $(MRUBY_BUILD_DEPEND_TARGETS)
+	@if [ -f .mruby_version ]; then \
+		built_version=`cat .mruby_version`; \
+		current_version=`git log -1 --format="%H" mruby`; \
+		if [ $$built_version != $$current_version ]; then \
+			echo $$current_version > .mruby_version; \
+			cd $(MRUBY_ROOT) && rm -rf build; \
+		fi; \
+	else \
+		git log -1 --format="%H" mruby > .mruby_version; \
+	fi
 	cd $(MRUBY_ROOT) && $(RAKE) MRUBY_CONFIG=$(NGX_MRUBY_ROOT)/build_config.rb NGX_MRUBY_CFLAGS="$(NGX_MRUBY_CFLAGS)"
 
 clean_mruby:
-	cd $(MRUBY_ROOT) && $(RAKE) deep_clean && rm -rf build
+	rm -f .mruby_version	
+	cd $(MRUBY_ROOT) && $(RAKE) MRUBY_CONFIG=$(NGX_MRUBY_ROOT)/build_config.rb deep_clean && rm -rf build
 
 $(MRUBY_MAK_FILE): build_mruby
 
diff --git a/build.sh b/build.sh
index 9c6daccd..eb2eabc1 100755
--- a/build.sh
+++ b/build.sh
@@ -87,13 +87,6 @@ else
     OPENSSL_BUILD_OPT=''
 fi
 
-# FIXME: not sure if we really need this. even if we do, it should be moved to mruby/Rakefile
-if [ -d "./mruby/${BUILD_DIR}" ]; then
-    echo "mruby Cleaning ..."
-    (cd mruby && rake clean MRUBY_CONFIG=../build_config.rb)
-    echo "mruby Cleaning ... Done"
-fi
-
 echo "ngx_mruby configure ..."
 ./configure ${CONFIG_OPT} --with-ngx-src-root=${NGINX_SRC} --with-ngx-config-opt="${NGINX_CONFIG_OPT}" ${OPENSSL_BUILD_OPT} $@
 echo "ngx_mruby configure ... Done"