diff --git a/stages/org.osbuild.ovf.meta.json b/stages/org.osbuild.ovf.meta.json
index 6799a06f..1f0fe8ce 100644
--- a/stages/org.osbuild.ovf.meta.json
+++ b/stages/org.osbuild.ovf.meta.json
@@ -40,7 +40,8 @@
               "default": "OtherLinux_64"
             },
             "mac_address": {
-              "type": "string"
+              "type": "string",
+              "pattern": "^[a-fA-F0-9]{12}$"
             }
           }
         }
diff --git a/stages/test/test_ovf.py b/stages/test/test_ovf.py
index 189cc97a..9285e63f 100644
--- a/stages/test/test_ovf.py
+++ b/stages/test/test_ovf.py
@@ -15,6 +15,8 @@ STAGE_NAME = "org.osbuild.ovf"
     ({"vmdk": "imagename"}, "'imagename' does not match '[a-zA-Z0-9+_.-]+.vmdk'"),
     ({"vmdk": "imagename.vmdk", "vmware": {"os_type": 1}}, "is not of type 'string'"),
     ({"vmdk": "imagename.vmdk", "virtualbox": {"os_type": 1}}, "is not of type 'string'"),
+    ({"vmdk": "imagename.vmdk", "virtualbox": {"mac_address": 1}}, "is not of type 'string'"),
+    ({"vmdk": "imagename.vmdk", "virtualbox": {"mac_address": "1"}}, "'1' does not match '^[a-fA-F0-9]{12}$'"),
     # Good API parameters
     ({"vmdk": "imagename.vmdk"}, ""),
     ({"vmdk": "imagename.vmdk", "vmware": {"os_type": "OtherGuest"}, "virtualbox": {"os_type": "OtherGuest"}}, ""),
@@ -46,7 +48,7 @@ def test_schema_validation_ovf(stage_schema, test_data, expected_err):
     # Replacements
     ({"vmware": {"os_type": "my-vmware-os-type"}}, ["my-vmware-os-type"],),
     ({"virtualbox": {"os_type": "my-vbox-os-type"}}, ["my-vbox-os-type"],),
-    ({"virtualbox": {"mac_address": "my-mac-address"}}, ["my-mac-address"],),
+    ({"virtualbox": {"mac_address": "000000000000"}}, ["000000000000"],),
 ])
 def test_ovf_default_template(tmp_path, stage_module, test_opts, expected_substrings):
     faked_vmdk_path = tmp_path / "some-image.vmdk"