diff --git a/src/Makefile.am b/src/Makefile.am
index 73b0c05d..e3575669 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -148,7 +148,8 @@ nghttpx_CPPFLAGS = ${libnghttpx_a_CPPFLAGS}
 nghttpx_LDADD = libnghttpx.a ${LDADD}
 
 if HAVE_MRUBY
-nghttpx_CPPFLAGS += -I${top_srcdir}/third-party/mruby/include @LIBMRUBY_CFLAGS@
+libnghttpx_a_CPPFLAGS += \
+	-I${top_srcdir}/third-party/mruby/include @LIBMRUBY_CFLAGS@
 nghttpx_LDADD += -L${top_builddir}/third-party/mruby/build/lib @LIBMRUBY_LIBS@
 endif # HAVE_MRUBY
 
diff --git a/third-party/Makefile.am b/third-party/Makefile.am
index 92d6fc4b..e90b297a 100644
--- a/third-party/Makefile.am
+++ b/third-party/Makefile.am
@@ -36,14 +36,15 @@ if HAVE_MRUBY
 
 mruby:
 	git submodule update --init
-	MRUBY_CONFIG=${srcdir}/build_config.rb \
-	BUILD_DIR=${abs_builddir}/mruby/build \
-	${srcdir}/mruby/minirake -f ${srcdir}/mruby/Rakefile
+	MRUBY_CONFIG="${srcdir}/build_config.rb" \
+	BUILD_DIR="${abs_builddir}/mruby/build" \
+	CC="${CC}" CXX="${CXX}" LD="${LD}" \
+	"${srcdir}/mruby/minirake" -f "${srcdir}/mruby/Rakefile"
 
 all-local: mruby
 
 clean-local:
-	-rm -rf ${abs_builddir}/mruby/build
+	-rm -rf "${abs_builddir}/mruby/build"
 
 endif # HAVE_MRUBY