diff -r 4fb829f8c04d Lib/tempfile.py
--- a/Lib/tempfile.py	Wed Mar 18 11:29:47 2015 +0100
+++ b/Lib/tempfile.py	Wed Mar 18 15:53:16 2015 +0100
@@ -426,7 +426,9 @@
 
     # iter() doesn't use __getattr__ to find the __iter__ method
     def __iter__(self):
-        return iter(self.file)
+        # don't return iter(self.file), but yield from it to avoid closing
+        # file as long as it's being used as iterator
+        yield from iter(self.file)
 
 
 def NamedTemporaryFile(mode='w+b', buffering=-1, encoding=None,
diff -r 4fb829f8c04d Lib/test/test_tempfile.py
--- a/Lib/test/test_tempfile.py	Wed Mar 18 11:29:47 2015 +0100
+++ b/Lib/test/test_tempfile.py	Wed Mar 18 15:53:16 2015 +0100
@@ -707,6 +707,13 @@
             # No reference cycle was created.
             self.assertIsNone(wr())
 
+    def test_iter(self):
+        # getting iterator from a temporary file should keep it alive
+        # as long as it's being iterated over
+        for l in tempfile.NamedTemporaryFile(mode='a+b'):
+            # if this doesn't raise, we're fine
+            pass
+
     def test_creates_named(self):
         # NamedTemporaryFile creates files with names
         f = tempfile.NamedTemporaryFile()