diff --git a/CHANGES.txt b/CHANGES.txt
index e3ad5e84c7..ba4347ec89 100644
--- a/CHANGES.txt
+++ b/CHANGES.txt
@@ -1,4 +1,5 @@
 2.1.10
+ * (cqlsh) Fix error when starting cqlsh with --debug (CASSANDRA-10282)
  * Scrub, Cleanup and Upgrade do not unmark compacting until all operations
    have completed, regardless of the occurence of exceptions (CASSANDRA-10274)
  * Fix handling of streaming EOF (CASSANDRA-10206)
diff --git a/bin/cqlsh b/bin/cqlsh
index 59496cee92..b5f5281516 100755
--- a/bin/cqlsh
+++ b/bin/cqlsh
@@ -2351,7 +2351,7 @@ def read_options(cmdlineargs, environment):
     try:
         options.connect_timeout = int(options.connect_timeout)
     except ValueError:
-        parser.error('{} is not a valid timeout.'.format(options.connect_timeout))
+        parser.error('"%s" is not a valid timeout.' % (options.connect_timeout,))
         options.connect_timeout = DEFAULT_CONNECT_TIMEOUT_SECONDS
 
     options.client_timeout = option_with_default(configs.get, 'connection', 'client_timeout', '10')
@@ -2447,8 +2447,8 @@ def main(options, hostname, port):
             sys.exit("Can't open %r: %s" % (options.file, e))
 
     if options.debug:
-        sys.stderr.write("Using CQL driver: {}\n".format(cassandra))
-        sys.stderr.write("Using connect timeout: {} seconds\n".format(options.connect_timeout))
+        sys.stderr.write("Using CQL driver: %s\n" % (cassandra,))
+        sys.stderr.write("Using connect timeout: %s seconds\n" % (options.connect_timeout,))
 
     try:
         shell = Shell(hostname,