diff --git a/swh/core/api/serializers.py b/swh/core/api/serializers.py
--- a/swh/core/api/serializers.py
+++ b/swh/core/api/serializers.py
@@ -53,7 +53,11 @@
 
 def dict_to_exception(exc_dict: Dict[str, Any]) -> Exception:
     temp = __import__(exc_dict["module"], fromlist=[exc_dict["type"]])
-    return getattr(temp, exc_dict["type"])(*exc_dict["args"])
+    try:
+        return getattr(temp, exc_dict["type"])(*exc_dict["args"])
+    except Exception:
+        # custom Exception type cannot be rebuilt, fallback to base Exception type
+        return Exception(exc_dict["message"])
 
 
 def encode_timedelta(td: datetime.timedelta) -> Dict[str, int]:
diff --git a/swh/core/api/tests/test_serializers.py b/swh/core/api/tests/test_serializers.py
--- a/swh/core/api/tests/test_serializers.py
+++ b/swh/core/api/tests/test_serializers.py
@@ -131,6 +131,12 @@
 }
 
 
+class ComplexExceptionType(Exception):
+    def __init__(self, error_type, message):
+        self.error_type = error_type
+        super().__init__(f"{error_type}: {message}")
+
+
 def test_serializers_round_trip_json():
     json_data = json_dumps(DATA)
     actual_data = json_loads(json_data)
@@ -153,6 +159,15 @@
     assert str(actual_data["exception"]) == error_message
 
 
+def test_complex_exception_serializer_round_trip_json():
+    exception = ComplexExceptionType("NotFound", "the object is missing")
+    json_data = json_dumps({"exception": exception})
+    actual_data = json_loads(json_data)
+    assert "exception" in actual_data
+    assert type(actual_data["exception"]) == Exception
+    assert str(actual_data["exception"]) == str(exception)
+
+
 def test_serializers_encode_swh_json():
     json_str = json_dumps(DATA)
     actual_data = json.loads(json_str)
@@ -187,6 +202,15 @@
     assert str(actual_data["exception"]) == error_message
 
 
+def test_complex_exception_serializer_round_trip_msgpack():
+    exception = ComplexExceptionType("NotFound", "the object is missing")
+    data = msgpack_dumps({"exception": exception})
+    actual_data = msgpack_loads(data)
+    assert "exception" in actual_data
+    assert type(actual_data["exception"]) == Exception
+    assert str(actual_data["exception"]) == str(exception)
+
+
 def test_serializers_generator_json():
     data = json_dumps((i for i in range(5)))
     assert json_loads(data) == [i for i in range(5)]