diff --git a/qubesusbproxy/core3ext.py b/qubesusbproxy/core3ext.py
index 799bff6..8ab6e5c 100644
--- a/qubesusbproxy/core3ext.py
+++ b/qubesusbproxy/core3ext.py
@@ -641,8 +641,11 @@ async def on_device_attach_usb(self, vm, event, device, options):
                         "qubes-usb-proxy not installed in the VM")
                 else:
                     # TODO: sanitize and include stdout
+                    sanitized_stderr = e.stderr.replace("\n", ", ")
+                    if sanitized_stderr.endswith(", "):
+                        sanitized_stderr = santizied_stderr[:-2] + "."
                     sanitized_stderr = ''.join(
-                        [chr(c) for c in e.stderr if 0x20 <= c < 0x80])
+                        [chr(c) for c in sanitized_stderr if 0x20 <= c < 0x80])
                     raise QubesUSBException(
                         'Device attach failed: {}'.format(sanitized_stderr))
         finally: