1 files changed, 17 insertions, 2 deletions

diff --git a/lib/libc/stdio/fflush.c b/lib/libc/stdio/fflush.c
index 4a5cf0f43084..fce893292e60 100644
--- a/lib/libc/stdio/fflush.c
+++ b/lib/libc/stdio/fflush.c
@@ -41,21 +41,36 @@ static char sccsid[] = "@(#)fflush.c	8.1 (Berkeley) 6/4/93";
 #include <errno.h>
 #include <stdio.h>
 #include "local.h"
+#ifdef _THREAD_SAFE
+#include <pthread.h>
+#include "pthread_private.h"
+#endif
 
 /* Flush a single file, or (if fp is NULL) all files.  */
+int
 fflush(fp)
 	register FILE *fp;
 {
+	int retval;
 
 	if (fp == NULL)
 		return (_fwalk(__sflush));
+#ifdef _THREAD_SAFE
+	_thread_flockfile(fp,__FILE__,__LINE__);
+#endif
 	if ((fp->_flags & (__SWR | __SRW)) == 0) {
 		errno = EBADF;
-		return (EOF);
+		retval = EOF;
+	} else {
+		retval = __sflush(fp);
 	}
-	return (__sflush(fp));
+#ifdef _THREAD_SAFE
+	_thread_funlockfile(fp);
+#endif
+	return (retval);
 }
 
+int
 __sflush(fp)
 	register FILE *fp;
 {