diff -ur calamares-3.2.7/src/modules/unpackfs/main.py calamares-3.2.7-unpackfs-dev/src/modules/unpackfs/main.py

--- calamares-3.2.7/src/modules/unpackfs/main.py	2019-04-27 20:12:03.000000000 +0200

+++ calamares-3.2.7-unpackfs-dev/src/modules/unpackfs/main.py	2019-05-06 00:49:55.325039262 +0200

@@ -252,13 +252,19 @@

             subprocess.check_call(["mount",

                                    "--bind", entry.source,

                                    imgmountdir])

-        else:

+        elif os.path.isfile(entry.source):

             subprocess.check_call(["mount",

                                    entry.source,

                                    imgmountdir,

                                    "-t", entry.sourcefs,

                                    "-o", "loop"

                                    ])

+        else: # entry.source is a device

+            subprocess.check_call(["mount",

+                                   entry.source,

+                                   imgmountdir,

+                                   "-t", entry.sourcefs

+                                   ])

     def unpack_image(self, entry, imgmountdir):

         """