diff --git a/ChangeLog b/ChangeLog
index d65a634afc..68f0330fe2 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,13 @@
+Tue Jul 16 21:07:04 2013  Masaki Matsushita  <glass.saga@gmail.com>
+
+	* configure.in: check strcasecmp().
+
+	* include/ruby/ruby.h: use strcasecmp() as st_strcasecmp() if it
+	  exists.
+
+	* st.c (st_strcasecmp): define the function only if strcasecmp()
+	  doesn't exist.
+
 Tue Jul 16 20:21:28 2013  Tanaka Akira  <akr@fsij.org>
 
 	* bignum.c (bigsq): Renamed from bigsqr.
diff --git a/configure.in b/configure.in
index 48184e23cf..e19f7209f4 100644
--- a/configure.in
+++ b/configure.in
@@ -1823,6 +1823,7 @@ AC_CHECK_FUNCS(sigaltstack)
 AC_CHECK_FUNCS(sigprocmask)
 AC_CHECK_FUNCS(sinh)
 AC_CHECK_FUNCS(spawnv)
+AC_CHECK_FUNCS(strcasecmp)
 AC_CHECK_FUNCS(symlink)
 AC_CHECK_FUNCS(syscall)
 AC_CHECK_FUNCS(sysconf)
diff --git a/include/ruby/ruby.h b/include/ruby/ruby.h
index 2fd5981a67..df89b387dd 100644
--- a/include/ruby/ruby.h
+++ b/include/ruby/ruby.h
@@ -1808,7 +1808,11 @@ int rb_toupper(int c);
 #define TOUPPER(c) rb_toupper((unsigned char)(c))
 #define TOLOWER(c) rb_tolower((unsigned char)(c))
 
+#ifdef HAVE_STRCASECMP
+#define st_strcasecmp strcasecmp
+#else
 int st_strcasecmp(const char *s1, const char *s2);
+#endif
 int st_strncasecmp(const char *s1, const char *s2, size_t n);
 #define STRCASECMP(s1, s2) (st_strcasecmp((s1), (s2)))
 #define STRNCASECMP(s1, s2, n) (st_strncasecmp((s1), (s2), (n)))
diff --git a/st.c b/st.c
index e86171927b..fff79f5571 100644
--- a/st.c
+++ b/st.c
@@ -1524,6 +1524,7 @@ strhash(st_data_t arg)
 }
 #endif
 
+#ifndef HAVE_STRCASECMP
 int
 st_strcasecmp(const char *s1, const char *s2)
 {
@@ -1547,6 +1548,7 @@ st_strcasecmp(const char *s1, const char *s2)
         }
     }
 }
+#endif
 
 int
 st_strncasecmp(const char *s1, const char *s2, size_t n)