1 files changed, 4 insertions, 2 deletions

diff --git a/lib/libc/stdio/wbuf.c b/lib/libc/stdio/wbuf.c
index 847699ad7cf4..54da709e77f2 100644
--- a/lib/libc/stdio/wbuf.c
+++ b/lib/libc/stdio/wbuf.c
@@ -49,6 +49,8 @@ static const char rcsid[] =
  * Write the given character into the (probably full) buffer for
  * the given file.  Flush the buffer out if it is or becomes full,
  * or if c=='\n' and the file is line buffered.
+ *
+ * Non-MT-safe
  */
 int
 __swbuf(c, fp)
@@ -80,14 +82,14 @@ __swbuf(c, fp)
 	 */
 	n = fp->_p - fp->_bf._base;
 	if (n >= fp->_bf._size) {
-		if (fflush(fp))
+		if (__fflush(fp))
 			return (EOF);
 		n = 0;
 	}
 	fp->_w--;
 	*fp->_p++ = c;
 	if (++n == fp->_bf._size || (fp->_flags & __SLBF && c == '\n'))
-		if (fflush(fp))
+		if (__fflush(fp))
 			return (EOF);
 	return (c);
 }