diff --git a/gunicorn/http/unreader.py b/gunicorn/http/unreader.py
index 9aadfbcf..1138e02f 100644
--- a/gunicorn/http/unreader.py
+++ b/gunicorn/http/unreader.py
@@ -49,8 +49,10 @@ class Unreader:
         return data[:size]
 
     def unread(self, data):
-        self.buf.seek(0, os.SEEK_END)
+        rest = self.buf.getvalue()
+        self.buf = io.BytesIO()
         self.buf.write(data)
+        self.buf.write(rest)
 
 
 class SocketUnreader(Unreader):
diff --git a/tests/test_http.py b/tests/test_http.py
index 3aa4808f..94a3a9d3 100644
--- a/tests/test_http.py
+++ b/tests/test_http.py
@@ -137,6 +137,14 @@ def test_unreader_unread():
     assert b'hi there' in unreader.read()
 
 
+def test_unreader_unread_should_place_data_at_the_beginning_of_the_buffer():
+    unreader = IterUnreader([b"abc", b"def"])
+    ab = unreader.read(2)
+    unreader.unread(ab)
+
+    assert unreader.read(None) == b"abc"
+
+
 def test_unreader_read_zero_size():
     unreader = Unreader()
     unreader.chunk = mock.MagicMock(side_effect=[b'qwerty', b'asdfgh'])