diff --git a/moulinette/utils/process.py b/moulinette/utils/process.py
index 2765abbd..f66aa7ed 100644
--- a/moulinette/utils/process.py
+++ b/moulinette/utils/process.py
@@ -5,7 +5,7 @@ try:
 except ImportError:
     from shlex import quote # Python3 >= 3.3
 
-from .stream import start_async_file_reading
+from .stream import async_file_reading
 
 # Prevent to import subprocess only for common classes
 CalledProcessError = subprocess.CalledProcessError
@@ -29,8 +29,10 @@ def call_async_output(args, callback, **kwargs):
     """Run command and provide its output asynchronously
 
     Run command with arguments and wait for it to complete to return the
-    returncode attribute. The callback must take one byte string argument
-    and will be called each time the command produces some output.
+    returncode attribute. The `callback` can be a method or a 2-tuple of
+    methods - for stdout and stderr respectively - which must take one
+    byte string argument. It will be called each time the command produces
+    some output.
 
     The stdout and stderr additional arguments for the Popen constructor
     are not allowed as they are used internally.
@@ -48,23 +50,37 @@ def call_async_output(args, callback, **kwargs):
         if a in kwargs:
             raise ValueError('%s argument not allowed, '
                              'it will be overridden.' % a)
-    if not callable(callback):
-        raise ValueError('callback argument must be callable')
+
+    # Validate callback argument
+    if isinstance(callback, tuple):
+        if len(callback) != 2:
+            raise ValueError('callback argument should be a 2-tuple')
+        kwargs['stdout'] = kwargs['stderr'] = subprocess.PIPE
+        separate_stderr = True
+    elif callable(callback):
+        kwargs['stdout'] = subprocess.PIPE
+        kwargs['stderr'] = subprocess.STDOUT
+        separate_stderr = False
+        callback = (callback,)
+    else:
+        raise ValueError('callback argument must be callable or a 2-tuple')
 
     # Run the command
-    p = subprocess.Popen(args, stdout=subprocess.PIPE,
-                         stderr=subprocess.STDOUT, **kwargs)
+    p = subprocess.Popen(args, **kwargs)
 
-    # Wrap and get command output
-    reader, queue = start_async_file_reading(p.stdout)
-    while not reader.eof():
-        while not queue.empty():
-            line = queue.get()
-            try:
-                callback(line.rstrip())
-            except:
-                pass
-    reader.join()
+    # Wrap and get command outputs
+    stdout_reader, stdout_consum = async_file_reading(p.stdout, callback[0])
+    if separate_stderr:
+        stderr_reader, stderr_consum = async_file_reading(p.stderr, callback[1])
+        while not stdout_reader.eof() and not stderr_reader.eof():
+            time.sleep(.1)
+        stderr_reader.join()
+        stderr_consum.join()
+    else:
+        while not stdout_reader.eof():
+            time.sleep(.1)
+    stdout_reader.join()
+    stdout_consum.join()
     return p.poll()
 
 
diff --git a/moulinette/utils/stream.py b/moulinette/utils/stream.py
index 0e696f35..8986067a 100644
--- a/moulinette/utils/stream.py
+++ b/moulinette/utils/stream.py
@@ -1,10 +1,10 @@
-import threading
-import Queue
+from multiprocessing.process import Process
+from multiprocessing.queues import SimpleQueue
 
 
 # Read from a stream ---------------------------------------------------
 
-class AsynchronousFileReader(threading.Thread):
+class AsynchronousFileReader(Process):
     """
     Helper class to implement asynchronous reading of a file
     in a separate thread. Pushes read lines on a queue to
@@ -15,9 +15,10 @@ class AsynchronousFileReader(threading.Thread):
 
     """
     def __init__(self, fd, queue):
-        assert isinstance(queue, Queue.Queue)
+        assert hasattr(queue, 'put')
+        assert hasattr(queue, 'empty')
         assert callable(fd.readline)
-        threading.Thread.__init__(self)
+        Process.__init__(self)
         self._fd = fd
         self._queue = queue
 
@@ -33,13 +34,25 @@ class AsynchronousFileReader(threading.Thread):
     def join(self, timeout=None, close=True):
         """Close the file and join the thread."""
         if close:
+            self._queue.put(StopIteration)
             self._fd.close()
-        threading.Thread.join(self, timeout)
+        Process.join(self, timeout)
 
 
-def start_async_file_reading(fd):
+def consume_queue(queue, callback):
+    """Consume the queue and give content to the callback."""
+    while True:
+        line = queue.get()
+        if line:
+            if line == StopIteration:
+                break
+            callback(line)
+
+def async_file_reading(fd, callback):
     """Helper which instantiate and run an AsynchronousFileReader."""
-    queue = Queue.Queue()
+    queue = SimpleQueue()
     reader = AsynchronousFileReader(fd, queue)
     reader.start()
-    return (reader, queue)
+    consummer = Process(target=consume_queue, args=(queue, callback))
+    consummer.start()
+    return (reader, consummer)