diff --git a/poky/scripts/lib/wic/engine.py b/poky/scripts/lib/wic/engine.py
index edcfab3..f0c5ff0 100644
--- a/poky/scripts/lib/wic/engine.py
+++ b/poky/scripts/lib/wic/engine.py
@@ -284,8 +284,8 @@
             aname = "_%s" % name
             if aname not in self.__dict__:
                 setattr(self, aname, find_executable(name, self.paths))
-                if aname not in self.__dict__:
-                    raise WicError("Can't find executable {}".format(name))
+                if aname not in self.__dict__ or self.__dict__[aname] is None:
+                    raise WicError("Can't find executable '{}'".format(name))
             return self.__dict__[aname]
         return self.__dict__[name]
 
@@ -391,11 +391,8 @@
         def write_ptable(parts, target):
             with tempfile.NamedTemporaryFile(prefix="wic-sfdisk-", mode='w') as outf:
                 write_sfdisk_script(outf, parts)
-                cmd = "{} --no-reread {} < {} 2>/dev/null".format(self.sfdisk, target, outf.name)
-                try:
-                    subprocess.check_output(cmd, shell=True)
-                except subprocess.CalledProcessError as err:
-                    raise WicError("Can't run '{}' command: {}".format(cmd, err))
+                cmd = "{} --no-reread {} < {} ".format(self.sfdisk, target, outf.name)
+                exec_cmd(cmd, as_shell=True)
 
         if expand is None:
             sparse_copy(self.imagepath, target)
@@ -412,11 +409,14 @@
             for line in exec_cmd("{} -F {}".format(self.sfdisk, target)).splitlines():
                 if line.startswith("Unpartitioned space ") and line.endswith("sectors"):
                     free = int(line.split()[-2])
+                    # Align free space to a 2048 sector boundary. YOCTO #12840.
+                    free = free - (free % 2048)
             if free is None:
                 raise WicError("Can't get size of unpartitioned space")
 
             # calculate expanded partitions sizes
             sizes = {}
+            num_auto_resize = 0
             for num, part in enumerate(parts['partitiontable']['partitions'], 1):
                 if num in expand:
                     if expand[num] != 0: # don't resize partition if size is set to 0
@@ -426,10 +426,11 @@
                         sizes[num] = sectors
                 elif part['type'] != 'f':
                     sizes[num] = -1
+                    num_auto_resize += 1
 
             for num, part in enumerate(parts['partitiontable']['partitions'], 1):
                 if sizes.get(num) == -1:
-                    part['size'] += free // len(sizes)
+                    part['size'] += free // num_auto_resize
 
             # write resized partition table to the target
             write_ptable(parts, target)