diff --git a/swh/core/api/__init__.py b/swh/core/api/__init__.py
--- a/swh/core/api/__init__.py
+++ b/swh/core/api/__init__.py
@@ -12,7 +12,7 @@
 import requests
 import datetime
 
-from typing import ClassVar, Optional, Type
+from typing import Any, ClassVar, Optional, Type
 
 from flask import Flask, Request, Response, request, abort
 from .serializers import (decode_response,
@@ -76,7 +76,20 @@
 # base API classes
 
 class RemoteException(Exception):
-    pass
+    """raised when remote returned an out-of-band failure notification, e.g., as a
+    HTTP status code or serialized exception
+
+    Attributes:
+        response: HTTP response corresponding to the failure
+
+    """
+    def __init__(self, payload: Optional[Any] = None,
+                 response: Optional[requests.Response] = None):
+        if payload is not None:
+            super().__init__(payload)
+        else:
+            super().__init__()
+        self.response = response
 
 
 def remote_api_endpoint(path):
@@ -201,6 +214,7 @@
             **opts)
         if opts.get('stream') or \
            response.headers.get('transfer-encoding') == 'chunked':
+            self.raise_for_status(response)
             return response.iter_content(chunk_size)
         else:
             return self._decode_response(response)
@@ -215,6 +229,7 @@
             **opts)
         if opts.get('stream') or \
            response.headers.get('transfer-encoding') == 'chunked':
+            self.raise_for_status(response)
             return response.iter_content(chunk_size)
         else:
             return self._decode_response(response)
@@ -222,28 +237,46 @@
     def get_stream(self, endpoint, **opts):
         return self.get(endpoint, stream=True, **opts)
 
+    def raise_for_status(self, response) -> None:
+        """check response HTTP status code and raise an exception if it denotes an
+        error; do nothing otherwise
+
+        """
+        # XXX: unpickling below breaks language-independence and should be
+        # replaced by proper language-independent [de]serialization
+        status_code = response.status_code
+        status_class = response.status_code // 100
+
+        if status_code == 404:
+            raise RemoteException(payload='404 not found', response=response)
+
+        try:
+            if status_class == 4:
+                data = decode_response(response)
+                raise pickle.loads(data)
+
+            if status_class == 5:
+                data = decode_response(response)
+                if 'exception_pickled' in data:
+                    raise pickle.loads(data['exception_pickled'])
+                else:
+                    raise RemoteException(payload=data['exception'],
+                                          response=response)
+
+        except (TypeError, pickle.UnpicklingError):
+            raise RemoteException(payload=data, response=response)
+
+        if status_class != 2:
+            raise RemoteException(
+                payload=f'API HTTP error: {status_code} {response.content}',
+                response=response)
+
     def _decode_response(self, response):
         if response.status_code == 404:
             return None
-        if response.status_code == 500:
-            data = decode_response(response)
-            if 'exception_pickled' in data:
-                raise pickle.loads(data['exception_pickled'])
-            else:
-                raise RemoteException(data['exception'])
-
-        # XXX: this breaks language-independence and should be
-        # replaced by proper unserialization
-        if response.status_code == 400:
-            raise pickle.loads(decode_response(response))
-        elif response.status_code != 200:
-            raise RemoteException(
-                "Unexpected status code for API request: %s (%s)" % (
-                    response.status_code,
-                    response.content,
-                )
-            )
-        return decode_response(response)
+        else:
+            self.raise_for_status(response)
+            return decode_response(response)
 
     def __repr__(self):
         return '<{} url={}>'.format(self.__class__.__name__, self.url)
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
@@ -29,6 +29,8 @@
         r = msgpack_loads(response.content)
     elif content_type.startswith('application/json'):
         r = json.loads(response.text, cls=SWHJSONDecoder)
+    elif content_type.startswith('text/'):
+        r = response.text
     else:
         raise ValueError('Wrong content type `%s` for API response'
                          % content_type)