diff --git a/test/conftest.py b/test/conftest.py
index 1c89a548..bacc479f 100755
--- a/test/conftest.py
+++ b/test/conftest.py
@@ -58,6 +58,9 @@ def recording_server_fixture():
 def recording_server(responses):
     """Serve the given (status, body) responses, repeating the last one.
 
+    A response may also be (status, body, content_type) to override the
+    content type inferred from the body, e.g. to serve malformed JSON.
+
     Yields the endpoint along with the list of requests received so far.
     """
 
@@ -80,7 +83,8 @@ def do_POST(self):  # BaseHTTPRequestHandler dispatches on this name.
                 }
             )
 
-            status, payload = remaining.pop(0) if len(remaining) > 1 else remaining[0]
+            response = remaining.pop(0) if len(remaining) > 1 else remaining[0]
+            status, payload, *rest = response
 
             if isinstance(payload, str):
                 content_type = "text/plain"
@@ -89,6 +93,9 @@ def do_POST(self):  # BaseHTTPRequestHandler dispatches on this name.
                 content_type = "application/json"
                 body = json.dumps(payload).encode()
 
+            if rest:
+                content_type = rest[0]
+
             self.send_response(status)
             self.send_header("content-type", content_type)
             self.send_header("content-length", str(len(body)))
diff --git a/test/http_error_test.py b/test/http_error_test.py
index 27454229..d737cfcc 100644
--- a/test/http_error_test.py
+++ b/test/http_error_test.py
@@ -60,3 +60,50 @@ def test_seam_http_throws_http_error_on_non_standard_response(server):
         seam.devices.list()
 
     assert exc_info.value.response.status_code == 503
+
+
+# The fake cannot produce malformed error responses, so the recording server
+# drives the bodies that must fall through is_api_error_response and raise a
+# plain HTTPError rather than being parsed into a SeamHttpApiError.
+def test_seam_http_raises_http_error_on_non_json_response(recording_server):
+    with recording_server([(500, "Internal Server Error")]) as (endpoint, _):
+        seam = Seam.from_api_key("seam_apikey_token", endpoint=endpoint)
+
+        with pytest.raises(niquests.HTTPError) as exc_info:
+            seam.devices.list()
+
+    assert exc_info.value.response.status_code == 500
+
+
+def test_seam_http_raises_http_error_on_malformed_json(recording_server):
+    responses = [(500, "{invalid json", "application/json")]
+
+    with recording_server(responses) as (endpoint, _):
+        seam = Seam.from_api_key("seam_apikey_token", endpoint=endpoint)
+
+        with pytest.raises(niquests.HTTPError) as exc_info:
+            seam.devices.list()
+
+    assert exc_info.value.response.status_code == 500
+
+
+def test_seam_http_raises_http_error_on_json_without_error_object(recording_server):
+    with recording_server([(500, {"message": "Some error"})]) as (endpoint, _):
+        seam = Seam.from_api_key("seam_apikey_token", endpoint=endpoint)
+
+        with pytest.raises(niquests.HTTPError) as exc_info:
+            seam.devices.list()
+
+    assert exc_info.value.response.status_code == 500
+
+
+def test_seam_http_raises_http_error_on_error_object_without_type_and_message(
+    recording_server,
+):
+    with recording_server([(500, {"error": {"code": 500}})]) as (endpoint, _):
+        seam = Seam.from_api_key("seam_apikey_token", endpoint=endpoint)
+
+        with pytest.raises(niquests.HTTPError) as exc_info:
+            seam.devices.list()
+
+    assert exc_info.value.response.status_code == 500