diff --git a/releasetools/c1_edify_generator.py b/releasetools/c1_edify_generator.py
index a2ccc30..95bdf48 100755
--- a/releasetools/c1_edify_generator.py
+++ b/releasetools/c1_edify_generator.py
@@ -35,3 +35,12 @@ class EdifyGenerator(edify_generator.EdifyGenerator):
             ('assert(package_extract_file("%(image)s", "/tmp/%(image)s"),\n'
              '       write_raw_image("/tmp/%(image)s", "%(partition)s"),\n'
              '       delete("/tmp/%(image)s"));') % args)
+
+    def Unmount(self, mount_point):
+      """Unmount the partition with the given mount_point."""
+      fstab = self.info.get("fstab", None)
+      if fstab:
+        p = fstab[mount_point]
+        self.script.append('unmount("%s");' %
+								(p.mount_point))
+        self.mounts.add(p.mount_point)
diff --git a/releasetools/c1_ota_from_target_files b/releasetools/c1_ota_from_target_files
index bb6b61b..358b3b2 100755
--- a/releasetools/c1_ota_from_target_files
+++ b/releasetools/c1_ota_from_target_files
@@ -68,6 +68,7 @@ def WriteFullOTAPackage(input_zip, output_zip):
   if OPTIONS.wipe_user_data:
     script.FormatPartition("/data")
 
+  script.Unmount("/system")
   script.FormatPartition("/system")
   script.Mount("/system")
   script.UnpackPackageDir("recovery", "/system")