diff --git a/placement/go/seats/meshwants/contract.go b/placement/go/seats/meshwants/contract.go
index fc93351..74860fa 100644
--- a/placement/go/seats/meshwants/contract.go
+++ b/placement/go/seats/meshwants/contract.go
@@ -286,6 +286,12 @@ type WantsByWantNodeModuleValue struct {
 	Yes   string `json:"yes,omitempty"`
 }
 
+// The values of WantsByWantNodeModuleValue's backup.
+const (
+	WantsByWantNodeModuleValueBackupAgain = "again"
+	WantsByWantNodeModuleValueBackupSkip  = "skip"
+)
+
 // WantsByWantNodeNodeValue is one value of the state wants under the key want.<node>.node.
 type WantsByWantNodeNodeValue struct {
 	Composed string `json:"composed"`
diff --git a/placement/seats/mesh-wants/seat.json b/placement/seats/mesh-wants/seat.json
index 236ed60..ececc75 100644
--- a/placement/seats/mesh-wants/seat.json
+++ b/placement/seats/mesh-wants/seat.json
@@ -97,7 +97,11 @@
               },
               "backup": {
                 "type": "string",
-                "description": "again or skip"
+                "description": "again or skip",
+                "enum": [
+                  "again",
+                  "skip"
+                ]
               },
               "words": {
                 "type": "string"
diff --git a/placement/ts/seats/meshwants/src/index.ts b/placement/ts/seats/meshwants/src/index.ts
index ad3dab8..fe56a7d 100644
--- a/placement/ts/seats/meshwants/src/index.ts
+++ b/placement/ts/seats/meshwants/src/index.ts
@@ -149,7 +149,7 @@ export type PolicyChangedEvent = Record<string, unknown>;
 /** is one value of the state wants under the key want.<node>.<module>. */
 export interface WantsByWantNodeModuleValue {
   /** again or skip */
-  "backup"?: string;
+  "backup"?: "again" | "skip";
   "composed"?: string;
   "fp"?: string;
   "hold"?: boolean;