diff --git a/openeo_driver/ProcessGraphDeserializer.py b/openeo_driver/ProcessGraphDeserializer.py
index d55a9328..eaed4858 100644
--- a/openeo_driver/ProcessGraphDeserializer.py
+++ b/openeo_driver/ProcessGraphDeserializer.py
@@ -1872,7 +1872,7 @@ def evaluate_process_from_url(process_id: str, namespace: str, args: dict, env:
         raise OpenEOApiException(
             status_code=400,
             code="ProcessNamespaceInvalid",
-            message=f"The value passed for namespace '{namespace}' in process '{process_id}' is invalid: {e}",
+            message=f"Process '{process_id}' specified with invalid namespace '{namespace}': {e!r}",
         ) from e
 
     return _evaluate_process_graph_process(
diff --git a/openeo_driver/processgraph.py b/openeo_driver/processgraph.py
index b37392dc..7e8c31c4 100644
--- a/openeo_driver/processgraph.py
+++ b/openeo_driver/processgraph.py
@@ -64,7 +64,9 @@ def get_process_definition_from_url(process_id: str, url: str) -> ProcessDefinit
         spec = found[0]
     else:
         raise OpenEOApiException(
-            status_code=400, code="ProcessNotFound", message=f"Process {process_id!r} not found in {url!r}."
+            status_code=400,
+            code="ProcessNotFound",
+            message=f"No valid process definition for {process_id!r} found at {url!r}.",
         )
 
     return ProcessDefinition(
diff --git a/tests/test_views_execute.py b/tests/test_views_execute.py
index d189d929..3410537f 100644
--- a/tests/test_views_execute.py
+++ b/tests/test_views_execute.py
@@ -11,6 +11,7 @@
 from typing import Iterable, Optional
 from unittest import mock, skip
 from zipfile import ZipFile
+import http.client
 
 import geopandas as gpd
 import numpy as np
@@ -2708,8 +2709,9 @@ def test_discard_result(api):
             "https://oeo.test/u/42/udp/bbox_mol",
             {"https://oeo.test/u/42/udp/bbox_mol": 404},
             (
-                    400, "ProcessUnsupported",
-                    "'bbox_mol' is not available in namespace 'https://oeo.test/u/42/udp/bbox_mol'."
+                400,
+                "ProcessNamespaceInvalid",
+                "Process 'bbox_mol' specified with invalid namespace 'https://oeo.test/u/42/udp/bbox_mol': HTTPError('404 Client Error: Not Found for url: https://oeo.test/u/42/udp/bbox_mol')",
             ),
     ),
     (
@@ -2717,8 +2719,8 @@ def test_discard_result(api):
             {"https://oeo.test/u/42/udp/bbox_mol": {"foo": "bar"}},
             (
                 400,
-                "ProcessResourceInvalid",
-                "Failed to load process 'bbox_mol' from 'https://oeo.test/u/42/udp/bbox_mol': KeyError('id')",
+                "ProcessNotFound",
+                "No valid process definition for 'bbox_mol' found at 'https://oeo.test/u/42/udp/bbox_mol'.",
             ),
         ),
         (
@@ -2726,8 +2728,8 @@ def test_discard_result(api):
             {"https://oeo.test/u/42/udp/bbox_mol": '{"foo": invalid json'},
             (
                 400,
-                "ProcessResourceInvalid",
-                "Failed to load process 'bbox_mol' from 'https://oeo.test/u/42/udp/bbox_mol': JSONDecodeError",
+                "ProcessNamespaceInvalid",
+                "Process 'bbox_mol' specified with invalid namespace 'https://oeo.test/u/42/udp/bbox_mol': JSONDecodeError('Expecting value: line 1 column 9 (char 8)')",
             ),
         ),
         (
@@ -2737,7 +2739,11 @@ def test_discard_result(api):
                     "pg/1.0/udp/bbox_mol.json", preprocess=lambda t: t.replace("bbox_mol", "BBox_Mol")
                 )
             },
-            None,
+            (
+                400,
+                "ProcessIdMismatch",
+                "Mismatch between expected process 'bbox_mol' and process 'BBox_Mol' defined at 'https://share.example/u42/bbox_mol.json'.",
+            ),
         ),
         (
             "https://share.example/u42/bbox_mol.json",
@@ -2765,7 +2771,7 @@ def test_evaluate_process_from_url(api, requests_mock, namespace, url_mocks, exp
         elif isinstance(value, dict):
             requests_mock.get(url, json=value)
         elif value in [404, 500]:
-            requests_mock.get(url, status_code=value)
+            requests_mock.get(url, status_code=value, reason=http.client.responses.get(value))
         elif isinstance(value, tuple) and value[0] in [302]:
             status_code, target = value
             requests_mock.get(url, status_code=status_code, headers={"Location": target})