diff --git a/umodbus/client/serial/redundancy_check.py b/umodbus/client/serial/redundancy_check.py
index f228dce..e3e7a89 100644
--- a/umodbus/client/serial/redundancy_check.py
+++ b/umodbus/client/serial/redundancy_check.py
@@ -73,9 +73,11 @@ def validate_crc(msg):
     """
     if not struct.unpack('<H', get_crc(msg[:-2])) ==\
             struct.unpack('<H', msg[-2:]):
-        raise CRCError('CRC validation failed.')
+        raise CRCError(msg)
 
 
 class CRCError(Exception):
-    """ Valid error to raise when CRC isn't correct. """
-    pass
+    """CRC validation failed."""
+
+    def __str__(self):
+        return self.__doc__
diff --git a/umodbus/utils.py b/umodbus/utils.py
index 403e504..b3803a3 100644
--- a/umodbus/utils.py
+++ b/umodbus/utils.py
@@ -138,6 +138,6 @@ def recv_exactly(recv_fn, size):
     response = b''.join(chunks)
 
     if len(response) != size:
-        raise ValueError
+        raise ValueError(response)
 
     return response