diff --git a/packages/rum-legacy/src/boot/publicApi.spec.ts b/packages/rum-legacy/src/boot/publicApi.spec.ts
index 864de097d1..f05a7981ba 100644
--- a/packages/rum-legacy/src/boot/publicApi.spec.ts
+++ b/packages/rum-legacy/src/boot/publicApi.spec.ts
@@ -382,6 +382,41 @@ describe('public api', () => {
       expect(eventsOfType('error')[0].usr).toEqual({ id: 'u-1', name: 'Ada' })
     })
 
+    it('sends the user id, name and email as strings, as the modern bundle does', () => {
+      api.setUser({ id: 42, name: 7, email: 1, tier: 3 })
+      api.addError(new Error('boom'))
+      flush()
+
+      // The intake types these three as strings and rejects the whole event otherwise. Custom
+      // fields keep their type.
+      expect(eventsOfType('error')[0].usr).toEqual({ id: '42', name: '7', email: '1', tier: 3 })
+    })
+
+    it('converts a user property set on its own as well', () => {
+      api.setUserProperty('id', 42)
+      api.addError(new Error('boom'))
+      flush()
+
+      expect(eventsOfType('error')[0].usr).toEqual({ id: '42' })
+    })
+
+    it('leaves an empty user id alone rather than sending the string "null"', () => {
+      api.setUser({ id: null, name: 'Ada' })
+      api.addError(new Error('boom'))
+      flush()
+
+      expect(eventsOfType('error')[0].usr).toEqual({ id: null, name: 'Ada' })
+    })
+
+    it('sends the account id and name as strings', () => {
+      api.setAccount({ id: 9, name: 1 })
+      api.setAccountProperty('name', 2)
+      api.addError(new Error('boom'))
+      flush()
+
+      expect(eventsOfType('error')[0].account).toEqual({ id: '9', name: '2' })
+    })
+
     it('leaves out an account without an id, which the format would reject', () => {
       api.setAccount({ name: 'no id here' })
       api.addError(new Error('boom'))
diff --git a/packages/rum-legacy/src/boot/publicApi.ts b/packages/rum-legacy/src/boot/publicApi.ts
index 1a2ccd4d8d..bfb87c4965 100644
--- a/packages/rum-legacy/src/boot/publicApi.ts
+++ b/packages/rum-legacy/src/boot/publicApi.ts
@@ -38,6 +38,24 @@ type Context = { [key: string]: any }
 const TRACKING_CONSENT_GRANTED = 'granted'
 const TRACKING_CONSENT_NOT_GRANTED = 'not-granted'
 
+const USER_STRING_FIELDS = ['id', 'name', 'email']
+const ACCOUNT_STRING_FIELDS = ['id', 'name']
+
+/*
+ * The intake types these fields as strings and rejects the whole event when one is not, and pages
+ * commonly pass a numeric id. The modern bundle converts them for the same reason; empty values are
+ * left alone, as it does, rather than sent as "null" or "undefined".
+ */
+function stringifyFields(context: Context, keys: string[]): Context {
+  for (let i = 0; i < keys.length; i++) {
+    const value = context[keys[i]]
+    if (value !== undefined && value !== null && value !== '') {
+      context[keys[i]] = String(value)
+    }
+  }
+  return context
+}
+
 export function makeRumLegacyPublicApi() {
   let running: ReturnType<typeof start> | undefined
   let initConfiguration: LegacyInitConfiguration | undefined
@@ -303,11 +321,12 @@ export function makeRumLegacyPublicApi() {
     }),
 
     setUser: monitor((user: Context) => {
-      userContext = user ? shallowMerge(user, {}) : {}
+      userContext = stringifyFields(user ? shallowMerge(user, {}) : {}, USER_STRING_FIELDS)
     }),
     getUser: monitor(() => shallowMerge(userContext, {})),
     setUserProperty: monitor((key: string, value: any) => {
       userContext[key] = value
+      stringifyFields(userContext, USER_STRING_FIELDS)
     }),
     removeUserProperty: monitor((key: string) => {
       delete userContext[key]
@@ -317,11 +336,12 @@ export function makeRumLegacyPublicApi() {
     }),
 
     setAccount: monitor((account: Context) => {
-      accountContext = account ? shallowMerge(account, {}) : {}
+      accountContext = stringifyFields(account ? shallowMerge(account, {}) : {}, ACCOUNT_STRING_FIELDS)
     }),
     getAccount: monitor(() => shallowMerge(accountContext, {})),
     setAccountProperty: monitor((key: string, value: any) => {
       accountContext[key] = value
+      stringifyFields(accountContext, ACCOUNT_STRING_FIELDS)
     }),
     removeAccountProperty: monitor((key: string) => {
       delete accountContext[key]