diff --git a/mitmproxy/addons/modifyheaders.py b/mitmproxy/addons/modifyheaders.py
index 2e6eb8f60..d560f5986 100644
--- a/mitmproxy/addons/modifyheaders.py
+++ b/mitmproxy/addons/modifyheaders.py
@@ -53,7 +53,7 @@ def parse_modify_spec(option) -> ModifySpec:
     elif len(parts) == 3:
         flow_filter_pattern, subject, replacement = parts
     else:
-        raise ValueError(f"Invalid number of parameters (2 or 3 are expected)")
+        raise ValueError("Invalid number of parameters (2 or 3 are expected)")
 
     flow_filter = flowfilter.parse(flow_filter_pattern)
     if not flow_filter:
diff --git a/test/mitmproxy/utils/test_arg_check.py b/test/mitmproxy/utils/test_arg_check.py
index 8ab140770..2c3c0d221 100644
--- a/test/mitmproxy/utils/test_arg_check.py
+++ b/test/mitmproxy/utils/test_arg_check.py
@@ -24,8 +24,9 @@ from mitmproxy.utils import arg_check
                          'SPEC Format: "username:pass", "any" to accept any user/pass combination,\n'
                          '"@path" to use an Apache htpasswd file, or\n'
                          '"ldap[s]:url_server_ldap:dn_auth:password:dn_subtree" '
-                         'for LDAP authentication.')
-
+                         'for LDAP authentication.'),
+    (["--replacements"], "--replacements is deprecated.\n"
+                  "Please use `--modify-body` or `--modify-headers` instead."),
 ])
 def test_check_args(arg, output):
     f = io.StringIO()