diff --git a/labgrid/driver/usbstoragedriver.py b/labgrid/driver/usbstoragedriver.py
index 5ceec293d..87c75cbca 100644
--- a/labgrid/driver/usbstoragedriver.py
+++ b/labgrid/driver/usbstoragedriver.py
@@ -113,7 +113,7 @@ def write_files(self, sources, target, partition, target_is_directory=True):
 
                 args = ["cp", "-T", copied_sources[0], target_path]
 
-            processwrapper.check_output(self.storage.command_prefix + args)
+            processwrapper.check_output(self.storage.wrap_command(args))
             self.proxy.unmount(self.devpath)
         except:
             # We are going to die with an exception anyway, so no point in waiting
@@ -231,7 +231,7 @@ def get_size(self, partition=None):
         """
         args = ["cat", f"/sys/class/block/{self._get_devpath(partition)[5:]}/size"]
         try:
-            size = subprocess.check_output(self.storage.command_prefix + args)
+            size = subprocess.check_output(self.storage.wrap_command(args))
         except subprocess.CalledProcessError:
             # while the medium is getting ready, the file does not yet exist
             return 0