1 files changed, 11 insertions, 1 deletions
diff --git a/newlib/libc/stdio/fflush.c b/newlib/libc/stdio/fflush.c
index b417e5424..05084dde0 100644
--- a/newlib/libc/stdio/fflush.c
+++ b/newlib/libc/stdio/fflush.c
@@ -72,8 +72,18 @@ _DEFUN(fflush, (fp),
   _flockfile (fp);
 
   t = fp->_flags;
-  if ((t & __SWR) == 0 || (p = fp->_bf._base) == NULL)
+  if ((t & __SWR) == 0)
     {
+      /* For a read stream, an fflush causes the next seek to be
+         unoptimized (i.e. forces a system-level seek).  This conforms
+         to the POSIX and SUSv3 standards.  */
+      fp->_flags |= __SNPT;
+      _funlockfile (fp);
+      return 0;
+    }
+  if ((p = fp->_bf._base) == NULL)
+    {
+      /* Nothing to flush.  */
       _funlockfile (fp);
       return 0;
     }