diff --git a/gunicorn/http/body.py b/gunicorn/http/body.py
index 2b7873d9..0c82c25a 100644
--- a/gunicorn/http/body.py
+++ b/gunicorn/http/body.py
@@ -113,11 +113,13 @@ class LengthReader(object):
     def read(self, size):
         if not isinstance(size, (int, long)):
             raise TypeError("size must be an integral type")
+        
+        size = min(self.length, size)
         if size < 0:
             raise ValueError("Size must be positive.")
         if size == 0:
             return ""
-        size = min(self.length, size)
+        
         
         buf = StringIO()
         data = self.unreader.read()