diff --git a/gunicorn/util.py b/gunicorn/util.py
index 54740421..f4f81066 100644
--- a/gunicorn/util.py
+++ b/gunicorn/util.py
@@ -90,8 +90,11 @@ def close(sock):
         pass
   
 def read_partial(sock, length, buf=None):
-    if buf is not None and len(buf) >= length:
-        return buf
+    if buf is not None:
+        if len(buf) >= length:
+            return buf
+        else:
+            length = length - len(buf)
 
     tmp_buf = sock.recv(length)