--- a/lib/strftime.c
+++ b/lib/strftime.c
@@ -18,14 +18,11 @@
    along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
 
 #ifdef _LIBC
-# define HAVE_MBLEN 1
-# define HAVE_MBRLEN 1
 # define HAVE_STRUCT_ERA_ENTRY 1
 # define HAVE_TM_GMTOFF 1
 # define HAVE_TM_ZONE 1
 # define HAVE_TZNAME 1
 # define HAVE_TZSET 1
-# define MULTIBYTE_IS_FORMAT_SAFE 1
 # include "../locale/localeinfo.h"
 #else
 # include <config.h>
@@ -44,10 +41,16 @@
 /* Do multibyte processing if multibytes are supported, unless
    multibyte sequences are safe in formats.  Multibyte sequences are
    safe if they cannot contain byte sequences that look like format
-   conversion specifications.  The GNU C Library uses UTF8 multibyte
-   encoding, which is safe for formats, but strftime.c can be used
-   with other C libraries that use unsafe encodings.  */
-#define DO_MULTIBYTE (HAVE_MBLEN && ! MULTIBYTE_IS_FORMAT_SAFE)
+   conversion specifications.  The multibyte encodings used by the
+   C library on the various platforms (UTF-8, GB2312, GBK, CP936,
+   GB18030, EUC-TW, BIG5, BIG5-HKSCS, CP950, EUC-JP, EUC-KR, CP949,
+   SHIFT_JIS, CP932, JOHAB) are safe for formats, because the byte '%'
+   cannot occur in a multibyte character except in the first byte.
+   But this does not hold for the DEC-HANYU encoding used on OSF/1.  */
+#if !defined __osf__
+# define MULTIBYTE_IS_FORMAT_SAFE 1
+#endif
+#define DO_MULTIBYTE (! MULTIBYTE_IS_FORMAT_SAFE)
 
 #if DO_MULTIBYTE
 # include <wchar.h>