diff --git a/Lib/smtplib.py b/Lib/smtplib.py
index 7b97a6a..13c56e1 100644
--- a/Lib/smtplib.py
+++ b/Lib/smtplib.py
@@ -364,8 +364,10 @@
         while 1:
             try:
                 line = self.file.readline()
-            except socket.error:
-                line = ''
+            except socket.error as e:
+                self.close()
+                raise SMTPServerDisconnected("Connection unexpectedly closed: "
+                                             + str(e))
             if not line:
                 self.close()
                 raise SMTPServerDisconnected("Connection unexpectedly closed")