diff --git a/onelogin/models/user.py b/onelogin/models/user.py
index dbe18d5c..e9dde0e5 100644
--- a/onelogin/models/user.py
+++ b/onelogin/models/user.py
@@ -37,7 +37,7 @@ class User(BaseModel):
     directory_id: Optional[StrictInt] = Field(None, description="The ID of the OneLogin Directory of the user.")
     trusted_idp_id: Optional[StrictInt] = Field(None, description="The ID of the OneLogin Trusted IDP of the user.")
     manager_ad_id: Optional[StrictStr] = Field(None, description="The ID of the user's manager in Active Directory.")
-    manager_user_id: Optional[StrictInt] = Field(None, description="The OneLogin User ID for the user's manager.")
+    manager_user_id: Optional[StrictStr] = Field(None, description="The OneLogin User ID for the user's manager.")
     samaccountname: Optional[StrictStr] = Field(None, description="The user's Active Directory username.")
     member_of: Optional[StrictStr] = Field(None, description="The user's directory membership.")
     userprincipalname: Optional[StrictStr] = Field(None, description="The principle name of the user.")
diff --git a/test/test_user_manager_user_id_fix.py b/test/test_user_manager_user_id_fix.py
new file mode 100644
index 00000000..80a3cb8d
--- /dev/null
+++ b/test/test_user_manager_user_id_fix.py
@@ -0,0 +1,114 @@
+# coding: utf-8
+
+"""
+    OneLogin API
+
+    OpenAPI Specification for OneLogin  # noqa: E501
+
+    The version of the OpenAPI document: 3.1.1
+    Generated by OpenAPI Generator (https://openapi-generator.tech)
+
+    Do not edit the class manually.
+"""
+
+
+import unittest
+import datetime
+
+import onelogin
+from onelogin.models.user import User  # noqa: E501
+from onelogin.rest import ApiException
+
+
+class TestUserManagerUserIdFix(unittest.TestCase):
+    """Test case for manager_user_id field fix (GitHub issue #100)"""
+
+    def setUp(self):
+        pass
+
+    def tearDown(self):
+        pass
+
+    def test_manager_user_id_with_string_value(self):
+        """
+        Test that manager_user_id accepts string values from API response.
+        This test validates the fix for GitHub issue #100 where API returns
+        manager_user_id as string but model expected integer.
+        """
+        user_data = {
+            "id": 123,
+            "username": "testuser",
+            "email": "test@example.com",
+            "manager_user_id": "252462756"  # String value as returned by API
+        }
+        
+        # This should work without validation errors
+        user = User.from_dict(user_data)
+        self.assertEqual(user.manager_user_id, "252462756")
+        self.assertIsInstance(user.manager_user_id, str)
+
+    def test_manager_user_id_with_none_value(self):
+        """
+        Test that manager_user_id accepts None values.
+        """
+        user_data = {
+            "id": 123, 
+            "username": "testuser",
+            "email": "test@example.com",
+            "manager_user_id": None
+        }
+        
+        user = User.from_dict(user_data)
+        self.assertIsNone(user.manager_user_id)
+
+    def test_manager_user_id_missing_field(self):
+        """
+        Test that manager_user_id can be omitted (defaults to None).
+        """
+        user_data = {
+            "id": 123,
+            "username": "testuser", 
+            "email": "test@example.com"
+            # manager_user_id field is omitted
+        }
+        
+        user = User.from_dict(user_data)
+        self.assertIsNone(user.manager_user_id)
+
+    def test_user_serialization_with_manager_user_id(self):
+        """
+        Test that User can be serialized back to dict with manager_user_id.
+        """
+        user_data = {
+            "id": 123,
+            "username": "testuser",
+            "email": "test@example.com", 
+            "manager_user_id": "252462756"
+        }
+        
+        user = User.from_dict(user_data)
+        user_dict = user.to_dict()
+        
+        self.assertEqual(user_dict["manager_user_id"], "252462756")
+        self.assertIsInstance(user_dict["manager_user_id"], str)
+
+    def test_parse_obj_compatibility(self):
+        """
+        Test that parse_obj method (used in API deserialization) works correctly.
+        This specifically tests the flow mentioned in the original issue traceback.
+        """
+        user_data = {
+            "id": 123,
+            "username": "testuser",
+            "email": "test@example.com", 
+            "manager_user_id": "252462756"
+        }
+        
+        # This is the method called in the traceback from the original issue
+        user = User.parse_obj(user_data)
+        self.assertEqual(user.manager_user_id, "252462756")
+        self.assertIsInstance(user.manager_user_id, str)
+
+
+if __name__ == '__main__':
+    unittest.main()
\ No newline at end of file