diff --git a/configure.in b/configure.in
index 33acfa60..474d6e23 100644
--- a/configure.in
+++ b/configure.in
@@ -3,7 +3,6 @@ AM_INIT_AUTOMAKE(msgpack, 0.1.0)
 AC_CONFIG_HEADER(config.h)
 
 AC_PROG_LIBTOOL
-#AC_CHECK_PROG(RUBY, ruby, ruby, [$PATH])
 
 AC_CONFIG_SUBDIRS([c cpp])
 AC_OUTPUT([Makefile])
diff --git a/cpp/Makefile.am b/cpp/Makefile.am
index e244763f..61a616aa 100644
--- a/cpp/Makefile.am
+++ b/cpp/Makefile.am
@@ -30,7 +30,7 @@ unpack.lo: msgpack/type/tuple.hpp
 zone.lo: msgpack/type/tuple.hpp
 
 msgpack/type/tuple.hpp: msgpack/type/tuple.hpp.erb
-	erb $< > $@
+	$(ERB) $< > $@
 
 MOSTLYCLEANFILES = msgpack/type/tuple.hpp
 
diff --git a/cpp/configure.in b/cpp/configure.in
index a60a489a..2c3e5d07 100644
--- a/cpp/configure.in
+++ b/cpp/configure.in
@@ -9,7 +9,11 @@ fi
 
 AC_PROG_CXX
 AC_PROG_LIBTOOL
-AC_CHECK_PROG(ERB, erb, erb, [$PATH])
+
+AC_CHECK_PROG(ERB, erb, erb)
+if test "x$ERB" = x; then
+	AC_MSG_ERROR([cannot find erb. Ruby is needed to build.])
+fi
 
 AC_CHECK_LIB(stdc++, main)
 
diff --git a/cpp/type/map.hpp b/cpp/type/map.hpp
index 3b544df9..c79f31c4 100644
--- a/cpp/type/map.hpp
+++ b/cpp/type/map.hpp
@@ -21,6 +21,7 @@
 #include "msgpack/object.hpp"
 #include <map>
 #include <vector>
+#include <algorithm>
 
 namespace msgpack {