diff --git a/llmlingua/prompt_compressor.py b/llmlingua/prompt_compressor.py
index 84e390e..fbc97ad 100644
--- a/llmlingua/prompt_compressor.py
+++ b/llmlingua/prompt_compressor.py
@@ -533,7 +533,7 @@ def compress_prompt(
                 - "rate" (str): The compression rate achieved, in a human-readable format.
                 - "saving" (str): Estimated savings in GPT-4 token usage.
         """
-        if self.use_llmlingua2:
+        if self.use_llmlingua2 or self.use_slingua:
             return self.compress_prompt_llmlingua2(
                 context,
                 rate=rate,
diff --git a/tests/test_slingua_routing.py b/tests/test_slingua_routing.py
new file mode 100644
index 0000000..a114d59
--- /dev/null
+++ b/tests/test_slingua_routing.py
@@ -0,0 +1,102 @@
+# Copyright (c) 2023 Microsoft
+# Licensed under The MIT License [see LICENSE for details]
+
+"""
+Unit tests for issue #235: use_slingua=True should route compress_prompt
+to compress_prompt_llmlingua2, just like use_llmlingua2=True does.
+
+These tests use sys.modules patching to avoid requiring ML dependencies
+(torch, transformers) to be installed.
+"""
+
+import sys
+import types
+import unittest
+from unittest.mock import MagicMock
+
+
+def _install_mock_modules():
+    """Insert lightweight stubs for heavy ML dependencies before importing llmlingua.
+
+    Note: patching sys.modules here is process-local. pytest --dist=loadfile
+    (used in the Makefile) ensures this file runs in its own worker, so the
+    stubs do not leak into integration tests that load real models.
+    """
+    for mod_name in [
+        "torch",
+        "torch.nn",
+        "torch.nn.functional",
+        "torch.utils",
+        "torch.utils.data",
+        "transformers",
+        "numpy",
+        "numpy.linalg",
+        "nltk",
+        "nltk.tokenize",
+        "accelerate",
+        "tiktoken",
+        "yaml",
+    ]:
+        if mod_name not in sys.modules:
+            sys.modules[mod_name] = MagicMock()
+
+
+_install_mock_modules()
+
+# Now the import will succeed with the stubs in place
+from llmlingua.prompt_compressor import PromptCompressor  # noqa: E402
+
+
+class SLinguaRoutingTester(unittest.TestCase):
+    """
+    Verifies that compress_prompt routes to compress_prompt_llmlingua2 when
+    use_slingua=True, without requiring a real model download.
+    """
+
+    def _make_compressor(self, use_llmlingua2=False, use_slingua=False):
+        """Return a PromptCompressor with model loading stubbed out."""
+        compressor = PromptCompressor.__new__(PromptCompressor)
+        compressor.use_llmlingua2 = use_llmlingua2
+        compressor.use_slingua = use_slingua
+        compressor.oai_tokenizer = MagicMock()
+        return compressor
+
+    def test_use_slingua_routes_to_llmlingua2(self):
+        """compress_prompt must call compress_prompt_llmlingua2 when use_slingua=True."""
+        compressor = self._make_compressor(use_slingua=True)
+        fake_result = {"compressed_prompt": "test", "origin_tokens": 10}
+        compressor.compress_prompt_llmlingua2 = MagicMock(return_value=fake_result)
+
+        result = compressor.compress_prompt(["hello world"], rate=0.5)
+
+        compressor.compress_prompt_llmlingua2.assert_called_once()
+        self.assertEqual(result, fake_result)
+
+    def test_use_llmlingua2_routes_to_llmlingua2(self):
+        """Existing behaviour: compress_prompt routes to compress_prompt_llmlingua2 when use_llmlingua2=True."""
+        compressor = self._make_compressor(use_llmlingua2=True)
+        fake_result = {"compressed_prompt": "test", "origin_tokens": 10}
+        compressor.compress_prompt_llmlingua2 = MagicMock(return_value=fake_result)
+
+        result = compressor.compress_prompt(["hello world"], rate=0.5)
+
+        compressor.compress_prompt_llmlingua2.assert_called_once()
+        self.assertEqual(result, fake_result)
+
+    def test_neither_flag_does_not_route_to_llmlingua2(self):
+        """When neither use_slingua nor use_llmlingua2 is set, compress_prompt_llmlingua2 is NOT called."""
+        compressor = self._make_compressor()
+        compressor.compress_prompt_llmlingua2 = MagicMock()
+
+        # The LLMLingua-1 path will raise because model internals are stubs;
+        # what matters is that compress_prompt_llmlingua2 was never entered.
+        try:
+            compressor.compress_prompt(["hello world"], rate=0.5)
+        except Exception:
+            pass
+
+        compressor.compress_prompt_llmlingua2.assert_not_called()
+
+
+if __name__ == "__main__":
+    unittest.main()