diff --git a/mcp/tools/decisions.py b/mcp/tools/decisions.py
index b268cae3..57de2c3a 100644
--- a/mcp/tools/decisions.py
+++ b/mcp/tools/decisions.py
@@ -106,11 +106,20 @@ def handle_get_causal_chain(args: dict) -> dict:
             )
         except (ImportError, AttributeError):
             if hasattr(graph, "get_causal_chain"):
-                chain = graph.get_causal_chain(
-                    decision_id,
-                    direction=direction,
-                    max_depth=max_depth,
-                )
+                try:
+                    chain = graph.get_causal_chain(
+                        decision_id,
+                        direction=direction,
+                        max_depth=max_depth,
+                    )
+                except TypeError:
+                    try:
+                        chain = graph.get_causal_chain(
+                            decision_id,
+                            depth=max_depth,
+                        )
+                    except TypeError:
+                        chain = graph.get_causal_chain(decision_id)
             else:
                 return {
                     "error": "Causal chain analysis is not supported on this graph backend",
diff --git a/tests/test_mcp_decisions_causal_chain.py b/tests/test_mcp_decisions_causal_chain.py
index b8260a28..76e389c3 100644
--- a/tests/test_mcp_decisions_causal_chain.py
+++ b/tests/test_mcp_decisions_causal_chain.py
@@ -136,6 +136,58 @@ class TestMCPDecisionsCausalChain(unittest.TestCase):
             {"chain": ["dec_down_1", "dec_down_2"], "count": 2, "direction": "downstream"},
         )
 
+    @patch("mcp.tools.decisions.get_graph")
+    @patch("semantica.context.causal_analyzer.CausalChainAnalyzer")
+    def test_fallback_depth_kwarg_signature(self, mock_analyzer_cls, mock_get_graph):
+        """Verify fallback works for backends accepting 'depth' kwarg (like OpenClaw)."""
+        mock_analyzer_cls.side_effect = ImportError("mocked import error")
+
+        class OpenClawGraphMock:
+            def __init__(self):
+                self.calls = []
+
+            def get_causal_chain(self, node_id, depth=3):
+                self.calls.append((node_id, depth))
+                return ["openclaw_a", "openclaw_b"]
+
+        graph_mock = OpenClawGraphMock()
+        mock_get_graph.return_value = graph_mock
+
+        response = handle_get_causal_chain(
+            {"decision_id": "dec_606", "direction": "upstream", "max_depth": 4}
+        )
+        self.assertEqual(graph_mock.calls, [("dec_606", 4)])
+        self.assertNotIn("error", response)
+        self.assertEqual(
+            response,
+            {"chain": ["openclaw_a", "openclaw_b"], "count": 2, "direction": "upstream"},
+        )
+
+    @patch("mcp.tools.decisions.get_graph")
+    @patch("semantica.context.causal_analyzer.CausalChainAnalyzer")
+    def test_fallback_positional_only_signature(self, mock_analyzer_cls, mock_get_graph):
+        """Verify fallback works for backends accepting only positional decision_id."""
+        mock_analyzer_cls.side_effect = AttributeError("mocked attr error")
+
+        class PositionalOnlyGraphMock:
+            def __init__(self):
+                self.calls = []
+
+            def get_causal_chain(self, node_id):
+                self.calls.append(node_id)
+                return ["pos_node"]
+
+        graph_mock = PositionalOnlyGraphMock()
+        mock_get_graph.return_value = graph_mock
+
+        response = handle_get_causal_chain({"decision_id": "dec_707"})
+        self.assertEqual(graph_mock.calls, ["dec_707"])
+        self.assertNotIn("error", response)
+        self.assertEqual(
+            response,
+            {"chain": ["pos_node"], "count": 1, "direction": "downstream"},
+        )
+
 
 if __name__ == "__main__":
     unittest.main()