diff --git a/CHANGELOG.md b/CHANGELOG.md
index 91b938ef1..ca36f0b88 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -26,6 +26,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 - Fix band name support in `DataCube.band()` when no metadata is available ([#515](https://github.com/Open-EO/openeo-python-client/issues/515))
 - Support optional child callbacks in generated `openeo.processes`, e.g. `merge_cubes` ([#522]((https://github.com/Open-EO/openeo-python-client/issues/522)))
+- Fix broken pre-flight validation in `Connection.save_user_defined_process` ([#526](https://github.com/Open-EO/openeo-python-client/issues/526))
 
 
 ## [0.26.0] - 2023-11-27 - "SRR6" release
diff --git a/openeo/rest/udp.py b/openeo/rest/udp.py
index 5cac35347..7c1b84f2b 100644
--- a/openeo/rest/udp.py
+++ b/openeo/rest/udp.py
@@ -94,7 +94,7 @@ def store(
         # TODO: this "public" flag is not standardized yet EP-3609, https://github.com/Open-EO/openeo-api/issues/310
         process["public"] = public
 
-        self._connection._preflight_validation(pg_with_metadata=process)
+        self._connection._preflight_validation(pg_with_metadata={"process": process})
         self._connection.put(
             path="/process_graphs/{}".format(self.user_defined_process_id), json=process, expected_status=200
         )
diff --git a/tests/rest/test_udp.py b/tests/rest/test_udp.py
index d621d9e7f..3c5c9fdfc 100644
--- a/tests/rest/test_udp.py
+++ b/tests/rest/test_udp.py
@@ -14,7 +14,7 @@
 
 @pytest.fixture
 def con100(requests_mock):
-    requests_mock.get(API_URL + "/", json=build_capabilities(udp=True))
+    requests_mock.get(API_URL + "/", json=build_capabilities(udp=True, validation=True))
     con = openeo.connect(API_URL)
     return con
 
@@ -197,6 +197,43 @@ def check_body(request):
     assert adapter.called
 
 
+def test_store_with_validation(con100, requests_mock, caplog):
+    requests_mock.get(API_URL + "/processes", json={"processes": [{"id": "add"}]})
+    validation_mock = requests_mock.post(
+        API_URL + "/validation", json={"errors": [{"code": "TooComplex", "message": "Nope"}]}
+    )
+
+    two = {
+        "add": {
+            "process_id": "add",
+            "arguments": {
+                "x": 1,
+                "y": 1,
+            },
+            "result": True,
+        }
+    }
+
+    def check_body(request):
+        body = request.json()
+        assert body == {
+            "process_graph": two,
+            "public": False,
+        }
+        return True
+
+    udp_mock = requests_mock.put(API_URL + "/process_graphs/two", additional_matcher=check_body)
+
+    udp = con100.save_user_defined_process("two", two)
+    assert isinstance(udp, RESTUserDefinedProcess)
+
+    assert udp_mock.called
+    assert validation_mock.called
+    assert [(r.levelname, r.getMessage()) for r in caplog.records] == [
+        ("WARNING", "Preflight process graph validation raised: [TooComplex] Nope")
+    ]
+
+
 def test_update(con100, requests_mock):
     updated_udp = load_json_resource("data/1.0.0/udp_details.json")