diff --git a/specification/mixedreality/resource-manager/Microsoft.MixedReality/stable/2021-01-01/common.json b/specification/mixedreality/resource-manager/Microsoft.MixedReality/stable/2021-01-01/common.json
index 661c10fe5627..7c961faf2cd2 100644
--- a/specification/mixedreality/resource-manager/Microsoft.MixedReality/stable/2021-01-01/common.json
+++ b/specification/mixedreality/resource-manager/Microsoft.MixedReality/stable/2021-01-01/common.json
@@ -31,6 +31,7 @@
       "properties": {
         "serial": {
           "type": "integer",
+          "format": "int32",
           "enum": [
             1,
             2