diff --git a/osbuild/formats/v2.py b/osbuild/formats/v2.py
index 4b5190e7..94da3a7f 100644
--- a/osbuild/formats/v2.py
+++ b/osbuild/formats/v2.py
@@ -274,14 +274,16 @@ def load_mount(description: Dict, index: Index, stage: Stage):
     if name in stage.mounts:
         raise ValueError(f"Duplicated mount '{name}'")
 
-    source = description["source"]
-    target = description["target"]
+    source = description.get("source")
+    target = description.get("target")
 
     options = description.get("options", {})
 
-    device = stage.devices.get(source)
-    if not device:
-        raise ValueError(f"Unknown device '{source}' for mount '{name}'")
+    device = None
+    if source:
+        device = stage.devices.get(source)
+        if not device:
+            raise ValueError(f"Unknown device '{source}' for mount '{name}'")
 
     stage.add_mount(name, info, device, target, options)
 
diff --git a/osbuild/mounts.py b/osbuild/mounts.py
index 346a7a35..519fc743 100644
--- a/osbuild/mounts.py
+++ b/osbuild/mounts.py
@@ -35,8 +35,10 @@ class Mount:
     def calc_id(self):
         m = hashlib.sha256()
         m.update(json.dumps(self.info.name, sort_keys=True).encode())
-        m.update(json.dumps(self.device.id, sort_keys=True).encode())
-        m.update(json.dumps(self.target, sort_keys=True).encode())
+        if self.device:
+            m.update(json.dumps(self.device.id, sort_keys=True).encode())
+        if self.target:
+            m.update(json.dumps(self.target, sort_keys=True).encode())
         m.update(json.dumps(self.options, sort_keys=True).encode())
         return m.hexdigest()
 
diff --git a/schemas/osbuild2.json b/schemas/osbuild2.json
index 4d66c1bc..f08996c0 100644
--- a/schemas/osbuild2.json
+++ b/schemas/osbuild2.json
@@ -71,7 +71,7 @@
     "mount": {
       "title": "Mount point for a stage",
       "additionalProperties": false,
-      "required": ["name", "type", "source", "target"],
+      "required": ["name", "type"],
       "properties": {
         "name": { "type": "string" },
         "type": { "type": "string" },