diff --git a/tests/basic/test_models.py b/tests/basic/test_models.py
index a8f7c8d30..8820bda6b 100644
--- a/tests/basic/test_models.py
+++ b/tests/basic/test_models.py
@@ -208,6 +208,65 @@ class TestModels(unittest.TestCase):
             except OSError:
                 pass
 
+    @patch('aider.models.litellm.completion')
+    @patch.object(Model, 'token_count')
+    def test_ollama_num_ctx_set_when_missing(self, mock_token_count, mock_completion):
+        mock_token_count.return_value = 1000
+        
+        model = Model("ollama/llama3")
+        messages = [{"role": "user", "content": "Hello"}]
+        
+        model.send_completion(messages, functions=None, stream=False)
+        
+        # Verify num_ctx was calculated and added to call
+        expected_ctx = int(1000 * 1.25) + 8192  # 9442
+        mock_completion.assert_called_once_with(
+            model=model.name,
+            messages=messages,
+            stream=False,
+            temperature=ANY,
+            num_ctx=expected_ctx,
+            tools=None,
+            tool_choice=None,
+        )
+
+    @patch('aider.models.litellm.completion')
+    def test_ollama_uses_existing_num_ctx(self, mock_completion):
+        model = Model("ollama/llama3")
+        model.extra_params = {"num_ctx": 4096}
+        
+        messages = [{"role": "user", "content": "Hello"}]
+        model.send_completion(messages, functions=None, stream=False)
+        
+        # Should use provided num_ctx from extra_params
+        mock_completion.assert_called_once_with(
+            model=model.name,
+            messages=messages,
+            stream=False,
+            temperature=ANY,
+            num_ctx=4096,
+            tools=None,
+            tool_choice=None,
+        )
+
+    @patch('aider.models.litellm.completion')
+    def test_non_ollama_no_num_ctx(self, mock_completion):
+        model = Model("gpt-4")
+        messages = [{"role": "user", "content": "Hello"}]
+        
+        model.send_completion(messages, functions=None, stream=False)
+        
+        # Regular models shouldn't get num_ctx
+        mock_completion.assert_called_once_with(
+            model=model.name,
+            messages=messages,
+            stream=False,
+            temperature=ANY,
+            tools=None,
+            tool_choice=None,
+        )
+        self.assertNotIn('num_ctx', mock_completion.call_args.kwargs)
+
 
 if __name__ == "__main__":
     unittest.main()