diff --git a/smpplib/client.py b/smpplib/client.py
index 5b10fcd..4d0dda5 100644
--- a/smpplib/client.py
+++ b/smpplib/client.py
@@ -226,20 +226,32 @@ def send_pdu(self, p):
 
         return True
 
+    def _recv_exact(self, exact_size):
+        """
+        Keep reading from self._socket until exact_size bytes have been read
+        """
+        parts = []
+        received = 0
+        while received < exact_size:
+            try:
+                part = self._socket.recv(exact_size - received)
+            except socket.timeout:
+                raise
+            except socket.error as e:
+                self.logger.warning(e)
+                raise exceptions.ConnectionError()
+            if not part:
+                raise exceptions.ConnectionError()
+            received += len(part)
+            parts.append(part)
+        return b"".join(parts)
+
     def read_pdu(self):
         """Read PDU from the SMSC"""
 
         self.logger.debug('Waiting for PDU...')
 
-        try:
-            raw_len = self._socket.recv(4)
-        except socket.timeout:
-            raise
-        except socket.error as e:
-            self.logger.warning(e)
-            raise exceptions.ConnectionError()
-        if not raw_len:
-            raise exceptions.ConnectionError()
+        raw_len = self._recv_exact(4)
 
         try:
             length = struct.unpack('>L', raw_len)[0]
@@ -247,18 +259,7 @@ def read_pdu(self):
             self.logger.warning('Receive broken pdu... %s', repr(raw_len))
             raise exceptions.PDUError('Broken PDU')
 
-        raw_pdu = raw_len
-        while len(raw_pdu) < length:
-            try:
-                raw_pdu_part = self._socket.recv(length - len(raw_pdu))
-            except socket.timeout:
-                raise
-            except socket.error as e:
-                self.logger.warning(e)
-                raise exceptions.ConnectionError()
-            if not raw_pdu_part:
-                raise exceptions.ConnectionError()
-            raw_pdu += raw_pdu_part
+        raw_pdu = raw_len + self._recv_exact(length - 4)
 
         self.logger.debug('<<%s (%d bytes)', binascii.b2a_hex(raw_pdu), len(raw_pdu))