diff --git a/osbuild/objectstore.py b/osbuild/objectstore.py
index 2aad57b5..8fd8cf82 100644
--- a/osbuild/objectstore.py
+++ b/osbuild/objectstore.py
@@ -48,6 +48,7 @@ def umount(target, lazy=False):
     args = []
     if lazy:
         args += ["--lazy"]
+    subprocess.run(["sync", "-f", target], check=True)
     subprocess.run(["umount"] + args + [target], check=True)