diff --git a/ChangeLog b/ChangeLog
index 525c696b98..61050d6c9d 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+Sun Jun 10 18:31:42 2012  Yuki Sonoda (Yugui)  <yugui@yugui.jp>
+
+	* configure.in (RUBY_NACL): Warns if $PATH does not contain the path
+	  to NativeClient SDK. PATH variable redefinition in GNUmakefile does
+	  not work for GNU make 3.81.
+
 Sun Jun 10 17:54:36 2012  Nobuyoshi Nakada  <nobu@ruby-lang.org>
 
 	* gc.h (IS_STACK_DIR_UPPER): utility macro.
diff --git a/configure.in b/configure.in
index 973445f56f..d88d286691 100644
--- a/configure.in
+++ b/configure.in
@@ -108,9 +108,17 @@ AC_DEFUN([RUBY_NACL],
   if test -z "${NACL_TOOLCHAIN}"; then
     AC_MSG_ERROR([Unrecognized --host and --build combination or NaCl SDK is not installed])
   fi
-  PATH="${PATH}:${NACL_SDK_ROOT}/toolchain/${NACL_TOOLCHAIN}/bin"
   AC_MSG_RESULT(${NACL_TOOLCHAIN})
 
+  AC_MSG_CHECKING([path to SDK])
+  if echo -- "${PATH}" | grep -F "${NACL_SDK_ROOT}/toolchain/${NACL_TOOLCHAIN}/bin" > /dev/null; then
+    AC_MSG_RESULT([set])
+  else
+    AC_MSG_RESULT([no])
+    AC_MSG_WARN([Add "${NACL_SDK_ROOT}/toolchain/${NACL_TOOLCHAIN}/bin" to \$PATH])
+    PATH="${PATH}:${NACL_SDK_ROOT}/toolchain/${NACL_TOOLCHAIN}/bin"
+  fi
+
   AC_SUBST(NACL_TOOLCHAIN)
   AC_SUBST(NACL_SDK_ROOT)
   AC_SUBST(NACL_SDK_VARIANT, nacl_cv_build_variant)