diff -r a0e8f2d882a3 Lib/test/test_wsgiref.py
--- a/Lib/test/test_wsgiref.py	Mon Jun 30 20:00:03 2014 -0400
+++ b/Lib/test/test_wsgiref.py	Wed Jul 02 16:56:06 2014 -0600
@@ -627,6 +627,31 @@
         h.run(error_app)
         self.assertEqual(side_effects['close_called'], True)
 
+    def testHeadersOnError(self):
+        """Verifies that headers are buffered until after the first non-empty byte string"""
+        def app(e, s):
+            s('200 OK', [
+                ("Content-Type", "text/plain; charset=utf-8"),
+            ])
+            yield b''
+
+            try:
+                # produce an exception tuple, so we can re-call s_r
+                raise AssertionError("This should not be re-raised.")
+            except AssertionError:
+                s('200 OK', [
+                    ("Content-Type", "text/plain; charset=utf-8"),
+                ], sys.exc_info())
+            yield b"data"
+
+        h = TestHandler()
+        h.run(app)
+        self.assertEqual(b"Status: 200 OK\r\n"
+            b"Content-Type: text/plain; charset=utf-8\r\n"
+            b"\r\n"
+            b"data",
+            h.stdout.getvalue())
+
 
 def test_main():
     support.run_unittest(__name__)
diff -r a0e8f2d882a3 Lib/wsgiref/handlers.py
--- a/Lib/wsgiref/handlers.py	Mon Jun 30 20:00:03 2014 -0400
+++ b/Lib/wsgiref/handlers.py	Wed Jul 02 16:56:06 2014 -0600
@@ -269,7 +269,9 @@
             raise AssertionError("write() before start_response()")
 
         elif not self.headers_sent:
-            # Before the first output, send the stored headers
+            # Before the first non-empty output, send the stored headers
+            if len(data) == 0:
+                return
             self.bytes_sent = len(data)    # make sure we know content-length
             self.send_headers()
         else: