diff --git a/changelog.d/8872.bugfix b/changelog.d/8872.bugfix
new file mode 100644
index 0000000000..ed00b70a0f
--- /dev/null
+++ b/changelog.d/8872.bugfix
@@ -0,0 +1 @@
+Fix a bug where `PUT /_synapse/admin/v2/users/<user_id>` failed to create a new user when `avatar_url` is specified. Bug introduced in Synapse v1.9.0.
diff --git a/synapse/rest/admin/users.py b/synapse/rest/admin/users.py
index 90940ff185..88cba369f5 100644
--- a/synapse/rest/admin/users.py
+++ b/synapse/rest/admin/users.py
@@ -320,9 +320,9 @@ class UserRestServletV2(RestServlet):
                             data={},
                         )
 
-            if "avatar_url" in body and type(body["avatar_url"]) == str:
+            if "avatar_url" in body and isinstance(body["avatar_url"], str):
                 await self.profile_handler.set_avatar_url(
-                    user_id, requester, body["avatar_url"], True
+                    target_user, requester, body["avatar_url"], True
                 )
 
             ret = await self.admin_handler.get_user(target_user)
diff --git a/tests/rest/admin/test_user.py b/tests/rest/admin/test_user.py
index 35c546aa69..ba1438cdc7 100644
--- a/tests/rest/admin/test_user.py
+++ b/tests/rest/admin/test_user.py
@@ -561,7 +561,7 @@ class UserRestTestCase(unittest.HomeserverTestCase):
                 "admin": True,
                 "displayname": "Bob's name",
                 "threepids": [{"medium": "email", "address": "bob@bob.bob"}],
-                "avatar_url": None,
+                "avatar_url": "mxc://fibble/wibble",
             }
         )
 
@@ -578,6 +578,7 @@ class UserRestTestCase(unittest.HomeserverTestCase):
         self.assertEqual("email", channel.json_body["threepids"][0]["medium"])
         self.assertEqual("bob@bob.bob", channel.json_body["threepids"][0]["address"])
         self.assertEqual(True, channel.json_body["admin"])
+        self.assertEqual("mxc://fibble/wibble", channel.json_body["avatar_url"])
 
         # Get user
         request, channel = self.make_request(
@@ -592,6 +593,7 @@ class UserRestTestCase(unittest.HomeserverTestCase):
         self.assertEqual(True, channel.json_body["admin"])
         self.assertEqual(False, channel.json_body["is_guest"])
         self.assertEqual(False, channel.json_body["deactivated"])
+        self.assertEqual("mxc://fibble/wibble", channel.json_body["avatar_url"])
 
     def test_create_user(self):
         """
@@ -606,6 +608,7 @@ class UserRestTestCase(unittest.HomeserverTestCase):
                 "admin": False,
                 "displayname": "Bob's name",
                 "threepids": [{"medium": "email", "address": "bob@bob.bob"}],
+                "avatar_url": "mxc://fibble/wibble",
             }
         )
 
@@ -622,6 +625,7 @@ class UserRestTestCase(unittest.HomeserverTestCase):
         self.assertEqual("email", channel.json_body["threepids"][0]["medium"])
         self.assertEqual("bob@bob.bob", channel.json_body["threepids"][0]["address"])
         self.assertEqual(False, channel.json_body["admin"])
+        self.assertEqual("mxc://fibble/wibble", channel.json_body["avatar_url"])
 
         # Get user
         request, channel = self.make_request(
@@ -636,6 +640,7 @@ class UserRestTestCase(unittest.HomeserverTestCase):
         self.assertEqual(False, channel.json_body["admin"])
         self.assertEqual(False, channel.json_body["is_guest"])
         self.assertEqual(False, channel.json_body["deactivated"])
+        self.assertEqual("mxc://fibble/wibble", channel.json_body["avatar_url"])
 
     @override_config(
         {"limit_usage_by_mau": True, "max_mau_value": 2, "mau_trial_days": 0}