diff --git a/src/core/Schemas.ts b/src/core/Schemas.ts
index 8f202d9d0..3ea701d24 100644
--- a/src/core/Schemas.ts
+++ b/src/core/Schemas.ts
@@ -138,6 +138,8 @@ const SafeString = z
   )
   .max(1000);
 
+const PersistentIdSchema = z.string().uuid();
+
 const EmojiSchema = z
   .number()
   .nonnegative()
@@ -388,7 +390,7 @@ export const ClientLogMessageSchema = z.object({
   type: z.literal("log"),
   severity: z.nativeEnum(LogSeverity),
   log: ID,
-  persistentID: SafeString,
+  persistentID: PersistentIdSchema, // WARNING: PII
 });
 
 export const ClientPingMessageSchema = z.object({
@@ -404,7 +406,7 @@ export const ClientIntentMessageSchema = z.object({
 export const ClientJoinMessageSchema = z.object({
   type: z.literal("join"),
   clientID: ID,
-  persistentID: SafeString, // WARNING: PII
+  persistentID: PersistentIdSchema, // WARNING: PII
   gameID: ID,
   lastTurn: z.number(), // The last turn the client saw.
   username: SafeString,
@@ -424,7 +426,7 @@ export const PlayerRecordSchema = z.object({
   clientID: ID,
   username: SafeString,
   ip: SafeString.nullable(), // WARNING: PII
-  persistentID: SafeString, // WARNING: PII
+  persistentID: PersistentIdSchema, // WARNING: PII
 });
 
 export const GameRecordSchema = z.object({