diff --git a/praw/models/reddit/modmail.py b/praw/models/reddit/modmail.py
index 2325e426e..f7443f243 100644
--- a/praw/models/reddit/modmail.py
+++ b/praw/models/reddit/modmail.py
@@ -174,7 +174,8 @@ def highlight(self):
         """
         self._reddit.post(API_PATH["modmail_highlight"].format(id=self.id))
 
-    def mute(self, num_days=3):
+    @_deprecate_args("num_days")
+    def mute(self, *, num_days=3):
         """Mute the non-mod user associated with the conversation.
 
         :param num_days: Duration of mute in days. Valid options are ``3``, ``7``, or
@@ -190,7 +191,7 @@ def mute(self, num_days=3):
 
         .. code-block:: python
 
-            reddit.subreddit("test").modmail("2gmz").mute(7)
+            reddit.subreddit("test").modmail("2gmz").mute(num_days=7)
 
         """
         if num_days != 3:  # no need to pass params if it's the default
diff --git a/tests/integration/models/reddit/test_modmail.py b/tests/integration/models/reddit/test_modmail.py
index f9783f38e..f68773c93 100644
--- a/tests/integration/models/reddit/test_modmail.py
+++ b/tests/integration/models/reddit/test_modmail.py
@@ -1,4 +1,3 @@
-import sys
 from datetime import datetime
 from unittest import mock
 
@@ -40,22 +39,12 @@ def test_mute_duration(self, _):
         self.reddit.read_only = False
         conversation = self.reddit.subreddit("all").modmail("g46rw")
         with self.recorder.use_cassette("TestModmailConversation.test_mute_duration"):
-            conversation.mute(7)
+            conversation.mute(num_days=7)
             conversation = self.reddit.subreddit("all").modmail("g46rw")
             assert conversation.user.mute_status["isMuted"]
-            if sys.version_info >= (3, 7, 0):
-                diff = datetime.fromisoformat(
-                    conversation.user.mute_status["endDate"]
-                ) - datetime.fromisoformat(conversation.mod_actions[-1].date)
-            else:
-                end_date = "".join(
-                    conversation.user.mute_status["endDate"].rsplit(":", 1)
-                )
-                start_date = "".join(conversation.mod_actions[-1].date.rsplit(":", 1))
-                date_format = "%Y-%m-%dT%H:%M:%S.%f%z"
-                diff = datetime.strptime(end_date, date_format) - datetime.strptime(
-                    start_date, date_format
-                )
+            diff = datetime.fromisoformat(
+                conversation.user.mute_status["endDate"]
+            ) - datetime.fromisoformat(conversation.mod_actions[-1].date)
             assert diff.days == 6  # 6 here because it is not 7 whole days
 
     @mock.patch("time.sleep", return_value=None)