diff --git a/ChangeLog b/ChangeLog
index c2326d1626..8582d9b641 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,10 @@
+Sun Jan 10 15:45:10 2016  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* include/ruby/missing.h (explicit_bzero_by_memset_s): remove
+	  inline implementation by memset_s, which needs a macro before
+	  including headers and can cause problems in extension libraries
+	  by the order of the macro and headers.
+
 Sun Jan 10 13:41:36 2016  Eric Wong  <e@80x24.org>
 
 	* io.c (rb_deferr): remove long obsolete global
diff --git a/include/ruby/missing.h b/include/ruby/missing.h
index 8db33496ab..97091606b0 100644
--- a/include/ruby/missing.h
+++ b/include/ruby/missing.h
@@ -18,10 +18,6 @@ extern "C" {
 #endif
 #endif
 
-#ifndef __STDC_WANT_LIB_EXT1__
-#define __STDC_WANT_LIB_EXT1__ 1
-#endif
-
 #include "ruby/config.h"
 #include <stddef.h>
 #include <math.h> /* for INFINITY and NAN */
@@ -248,15 +244,7 @@ RUBY_EXTERN void setproctitle(const char *fmt, ...);
 
 #ifndef HAVE_EXPLICIT_BZERO
 RUBY_EXTERN void explicit_bzero(void *b, size_t len);
-# ifdef HAVE_MEMSET_S
-# include <string.h>
-static inline void
-explicit_bzero_by_memset_s(void *b, size_t len)
-{
-    memset_s(b, len, 0, len);
-}
-#   define explicit_bzero(b, len) explicit_bzero_by_memset_s(b, len)
-# elif defined SecureZeroMemory
+# if defined SecureZeroMemory
 #   define explicit_bzero(b, len) SecureZeroMemory(b, len)
 # endif
 #endif
diff --git a/missing/explicit_bzero.c b/missing/explicit_bzero.c
index 2409deca20..a7ff9cb517 100644
--- a/missing/explicit_bzero.c
+++ b/missing/explicit_bzero.c
@@ -1,5 +1,12 @@
+#ifndef __STDC_WANT_LIB_EXT1__
+#define __STDC_WANT_LIB_EXT1__ 1
+#endif
+
 #include "ruby/missing.h"
 #include <string.h>
+#ifdef HAVE_MEMSET_S
+# include <string.h>
+#endif
 
 #ifdef _WIN32
 #include <windows.h>