diff --git a/acme/acme/client.py b/acme/acme/client.py
index ee4cf7985..2e07d34d7 100644
--- a/acme/acme/client.py
+++ b/acme/acme/client.py
@@ -650,7 +650,7 @@ class ClientNetwork(object):  # pylint: disable=too-many-instance-attributes
                 raise # pragma: no cover
             else:
                 host, path, _err_no, err_msg = m.groups()
-                raise ValueError("Requesting {0}{1}: {2}".format(host, path, err_msg))
+                raise ValueError("Requesting {0}{1}:{2}".format(host, path, err_msg))
 
         # If content is DER, log the base64 of it instead of raw bytes, to keep
         # binary data out of the logs.