diff --git a/Lib/test/test_fileio.py b/Lib/test/test_fileio.py
index d8f6225..7a9b780 100644
--- a/Lib/test/test_fileio.py
+++ b/Lib/test/test_fileio.py
@@ -78,6 +78,9 @@
         self.assertEqual(self.f.readline(None), b"hi\n")
         self.assertEqual(self.f.readlines(None), [b"bye\n", b"abc"])
 
+    def test_reject(self):
+        self.assertRaises(TypeError, self.f.write, "Hello!")
+
     def testRepr(self):
         self.assertEquals(repr(self.f), "<_io.FileIO name=%r mode=%r>"
                                         % (self.f.name, self.f.mode))
@@ -170,7 +173,7 @@
 
     @ClosedFDRaises
     def testErrnoOnClosedWrite(self, f):
-        f.write('a')
+        f.write(b'a')
 
     @ClosedFDRaises
     def testErrnoOnClosedSeek(self, f):
diff --git a/Misc/NEWS b/Misc/NEWS
index befc61c..2a66d01 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -73,6 +73,8 @@
 Library
 -------
 
+- Issue #7785: Don't accept bytes in FileIO.write().
+
 - Issue #7773: Fix an UnboundLocalError in platform.linux_distribution() when
   the release file is empty.
 
diff --git a/Modules/_io/fileio.c b/Modules/_io/fileio.c
index 8162396..d04a74d 100644
--- a/Modules/_io/fileio.c
+++ b/Modules/_io/fileio.c
@@ -651,7 +651,7 @@
 	if (!self->writable)
 		return err_mode("writing");
 
-	if (!PyArg_ParseTuple(args, "s*", &pbuf))
+	if (!PyArg_ParseTuple(args, "y*", &pbuf))
 		return NULL;
 
 	if (_PyVerify_fd(self->fd)) {