diff --git a/limacharlie/sdk/cases.py b/limacharlie/sdk/cases.py
index 2cfd740..9487aa9 100644
--- a/limacharlie/sdk/cases.py
+++ b/limacharlie/sdk/cases.py
@@ -59,9 +59,11 @@ def create_case(
         """
         data: dict[str, Any] = {}
         if detection is not None:
-            # The extension schema declares detection as type "json",
-            # which the platform validates as a JSON string (not a dict).
-            data["detection"] = json.dumps(detection)
+            # Pass the detection dict directly — the gzdata encoding
+            # already JSON-serializes the full data dict, so json.dumps
+            # here would double-encode it into a string that the LC
+            # backend drops (schema type "json" expects an object).
+            data["detection"] = detection
         if severity is not None:
             data["severity"] = severity
         if summary is not None:
diff --git a/tests/unit/test_sdk_cases.py b/tests/unit/test_sdk_cases.py
index b3571a3..425eb2d 100644
--- a/tests/unit/test_sdk_cases.py
+++ b/tests/unit/test_sdk_cases.py
@@ -84,7 +84,7 @@ def test_calls_extension_request(self, cases, mock_org):
             MockExt.assert_called_once_with(mock_org)
             mock_ext.request.assert_called_once_with(
                 "ext-cases", "create_case",
-                data={"detection": json.dumps(self._SAMPLE_DETECTION)},
+                data={"detection": self._SAMPLE_DETECTION},
             )
             assert result["case_id"] == "tid-new"
 
@@ -100,7 +100,7 @@ def test_all_optional_fields(self, cases, mock_org):
             )
             call_data = mock_ext.request.call_args[1]["data"]
             assert call_data == {
-                "detection": json.dumps(self._SAMPLE_DETECTION),
+                "detection": self._SAMPLE_DETECTION,
                 "severity": "high",
                 "summary": "Test summary",
             }
@@ -144,7 +144,7 @@ def test_with_summary(self, cases, mock_org):
             )
             call_data = mock_ext.request.call_args[1]["data"]
             assert call_data == {
-                "detection": json.dumps(self._SAMPLE_DETECTION),
+                "detection": self._SAMPLE_DETECTION,
                 "severity": "high",
                 "summary": "Lateral movement detected",
             }