diff --git a/libc/stdio/vfprintf.c b/libc/stdio/vfprintf.c
index 9c36b79..dac8496 100644
--- a/libc/stdio/vfprintf.c
+++ b/libc/stdio/vfprintf.c
@@ -100,8 +100,8 @@
 	fake._lbfsize = 0;	/* not actually used, but Just In Case */
 
 	/* do the work, then copy any error status */
-	ret = vfprintf(&fake, fmt, ap);
-	if (ret >= 0 && fflush(&fake))
+	ret = __vfprintf(&fake, fmt, ap);
+	if (ret >= 0 && __sflush(&fake))
 		ret = EOF;
 	if (fake._flags & __SERR)
 		fp->_flags |= __SERR;
@@ -158,6 +158,17 @@
 int
 vfprintf(FILE *fp, const char *fmt0, __va_list ap)
 {
+	int ret;
+
+	FLOCKFILE(fp);
+	ret = __vfprintf(fp, fmt0, ap);
+	FUNLOCKFILE(fp);
+	return (ret);
+}
+
+int
+__vfprintf(FILE *fp, const char *fmt0, __va_list ap)
+{
 	char *fmt;	/* format string */
 	int ch;	/* character from fmt */
 	int n, m, n2;	/* handy integers (short term usage) */