diff --git a/smpplib/client.py b/smpplib/client.py
index bb44b04..5b10fcd 100644
--- a/smpplib/client.py
+++ b/smpplib/client.py
@@ -256,7 +256,7 @@ def read_pdu(self):
             except socket.error as e:
                 self.logger.warning(e)
                 raise exceptions.ConnectionError()
-            if not raw_pdu:
+            if not raw_pdu_part:
                 raise exceptions.ConnectionError()
             raw_pdu += raw_pdu_part