diff --git a/blivet/devices/partition.py b/blivet/devices/partition.py
index 504d7e178..5cccf4e0e 100644
--- a/blivet/devices/partition.py
+++ b/blivet/devices/partition.py
@@ -539,7 +539,7 @@ def _wipe(self):
         # Erase 1MiB or to end of partition
         count = min(int(Size("1 MiB") // bs), part_len)
 
-        cmd = ["dd", "if=/dev/zero", "of=%s" % device, "bs=%s" % bs,
+        cmd = ["dd", "if=/dev/zero", "of=%s" % device, "bs=%d" % int(bs),
                "seek=%s" % start, "count=%s" % count]
         try:
             util.run_program(cmd)