diff -r 5bd248c2cc75 Lib/http/client.py
--- a/Lib/http/client.py	Mon Dec 12 11:17:59 2016 -0800
+++ b/Lib/http/client.py	Mon Dec 12 23:38:30 2016 +0200
@@ -566,8 +566,8 @@
                 value.append(self._safe_read(chunk_left))
                 self.chunk_left = 0
             return b''.join(value)
-        except IncompleteRead:
-            raise IncompleteRead(b''.join(value))
+        except IncompleteRead as incomplete_read:
+            raise IncompleteRead(b''.join(value)) from incomplete_read
 
     def _readinto_chunked(self, b):
         assert self.chunked != _UNKNOWN