diff --git a/server/db/defaults.py b/server/db/defaults.py
index 1f752da4c..da597fc8a 100644
--- a/server/db/defaults.py
+++ b/server/db/defaults.py
@@ -51,14 +51,24 @@ def calculate_expiry_period(invitation, today=datetime.today()):
 
 
 def cleanse_short_name(data, attr="short_name"):
+    """
+    Cleanses a short_name attribute in a JSON object (typically a description of a CO).
+    :param data: The JSON object (CO)
+    :param attr: The attribute name
+    :return: True if the attribute was modified, False otherwise
+    """
     if attr not in data:
         raise BadRequest(f"Missing {attr} in JSON")
     short_name = data[attr]
     while short_name[0].isnumeric():
         short_name = short_name[1:]
 
-    data[attr] = re.sub(r"[^a-zA-Z_0-9]+", "", short_name).lower()[:16]
-    return data[attr] == short_name
+    short_name = re.sub(r"[^a-zA-Z_0-9]+", "", short_name).lower()[:16]
+
+    is_modified = not (data[attr] == short_name)
+    data[attr] = short_name
+
+    return not is_modified
 
 
 uri_re = re.compile("^(https?|ssh|ftp)://(.+)$")
diff --git a/server/test/api/test_collaboration.py b/server/test/api/test_collaboration.py
index e8da72649..bf3154573 100644
--- a/server/test/api/test_collaboration.py
+++ b/server/test/api/test_collaboration.py
@@ -692,7 +692,7 @@ def test_api_call_existing_short_name(self):
                                     data=json.dumps({
                                         "name": "new_collaboration",
                                         "administrators": ["the@ex.org"],
-                                        "short_name": f"1{ai_computing_short_name}",
+                                        "short_name": f"{ai_computing_short_name}",
                                         "description": "new_collaboration",
                                         "accepted_user_policy": "https://aup.org",
                                         "disable_join_requests": True,
@@ -748,6 +748,40 @@ def test_api_call_with_invalid_short_name(self):
         response_json = response.json
         self.assertTrue("Invalid CO short_name" in response_json["message"])
 
+    def test_api_call_with_invalid_short_name_2(self):
+        response = self.client.post("/api/collaborations/v1",
+                                    headers={"Authorization": f"Bearer {uuc_secret}"},
+                                    data=json.dumps({
+                                        "name": "new_collaboration",
+                                        "description": "new_collaboration",
+                                        "administrators": ["the@ex.org", "that@ex.org"],
+                                        "short_name": "lang56789012345678901234567890",
+                                        "disable_join_requests": True,
+                                        "disclose_member_information": True,
+                                        "disclose_email_information": True
+                                    }),
+                                    content_type="application/json")
+        self.assertEqual(400, response.status_code)
+        response_json = response.json
+        self.assertTrue("Invalid CO short_name" in response_json["message"])
+
+    def test_api_call_with_invalid_short_name_3(self):
+        response = self.client.post("/api/collaborations/v1",
+                                    headers={"Authorization": f"Bearer {uuc_secret}"},
+                                    data=json.dumps({
+                                        "name": "new_collaboration",
+                                        "description": "new_collaboration",
+                                        "administrators": ["the@ex.org", "that@ex.org"],
+                                        "short_name": "12begincijfer",
+                                        "disable_join_requests": True,
+                                        "disclose_member_information": True,
+                                        "disclose_email_information": True
+                                    }),
+                                    content_type="application/json")
+        self.assertEqual(400, response.status_code)
+        response_json = response.json
+        self.assertTrue("Invalid CO short_name" in response_json["message"])
+
     def test_collaborations_may_request_collaboration_true(self):
         self.login("urn:mary")
         res = self.get("/api/collaborations/may_request_collaboration", with_basic_auth=False)