diff --git a/posthog-core/src/index.ts b/posthog-core/src/index.ts
index 39ff6f12..bf4471e1 100644
--- a/posthog-core/src/index.ts
+++ b/posthog-core/src/index.ts
@@ -724,48 +724,52 @@ export abstract class PostHogCore extends PostHogCoreStateless {
   }
 
   protected setupBootstrap(options?: Partial<PostHogCoreOptions>): void {
+    const bootstrap = options?.bootstrap
+    if (!bootstrap) {
+      return
+    }
+
     // bootstrap options are only set if no persisted values are found
     // this is to prevent overwriting existing values
-    if (options?.bootstrap?.distinctId) {
-      if (options?.bootstrap?.isIdentifiedId) {
+    if (bootstrap.distinctId) {
+      if (bootstrap.isIdentifiedId) {
         const distinctId = this.getPersistedProperty(PostHogPersistedProperty.DistinctId)
 
         if (!distinctId) {
-          this.setPersistedProperty(PostHogPersistedProperty.DistinctId, options.bootstrap.distinctId)
+          this.setPersistedProperty(PostHogPersistedProperty.DistinctId, bootstrap.distinctId)
         }
       } else {
         const anonymousId = this.getPersistedProperty(PostHogPersistedProperty.AnonymousId)
 
         if (!anonymousId) {
-          this.setPersistedProperty(PostHogPersistedProperty.AnonymousId, options.bootstrap.distinctId)
+          this.setPersistedProperty(PostHogPersistedProperty.AnonymousId, bootstrap.distinctId)
         }
       }
     }
 
-    if (options?.bootstrap?.featureFlags) {
-      const bootstrapFlags = Object.keys(options.bootstrap?.featureFlags || {})
-        .filter((flag) => !!options.bootstrap?.featureFlags?.[flag])
+    const bootstrapfeatureFlags = bootstrap.featureFlags
+    if (bootstrapfeatureFlags && Object.keys(bootstrapfeatureFlags).length) {
+      const bootstrapFlags = Object.keys(bootstrapfeatureFlags)
+        .filter((flag) => !!bootstrapfeatureFlags[flag])
         .reduce(
-          (res: Record<string, string | boolean>, key) => (
-            (res[key] = options.bootstrap?.featureFlags?.[key] || false), res
-          ),
+          (res: Record<string, string | boolean>, key) => ((res[key] = bootstrapfeatureFlags[key] || false), res),
           {}
         )
 
-      if (bootstrapFlags.length) {
+      if (Object.keys(bootstrapFlags).length) {
         const currentFlags =
           this.getPersistedProperty<PostHogDecideResponse['featureFlags']>(PostHogPersistedProperty.FeatureFlags) || {}
         const newFeatureFlags = { ...bootstrapFlags, ...currentFlags }
         this.setKnownFeatureFlags(newFeatureFlags)
       }
 
-      const bootstrapFlagPayloads = options?.bootstrap?.featureFlagPayloads
-      if (bootstrapFlagPayloads && bootstrapFlagPayloads?.length) {
+      const bootstrapFlagPayloads = bootstrap.featureFlagPayloads
+      if (bootstrapFlagPayloads && Object.keys(bootstrapFlagPayloads).length) {
         const currentFlagPayloads =
           this.getPersistedProperty<PostHogDecideResponse['featureFlagPayloads']>(
             PostHogPersistedProperty.FeatureFlagPayloads
           ) || {}
-        const newFeatureFlagPayloads = { bootstrapFlagPayloads, ...currentFlagPayloads }
+        const newFeatureFlagPayloads = { ...bootstrapFlagPayloads, ...currentFlagPayloads }
         this.setKnownFeatureFlagPayloads(newFeatureFlagPayloads)
       }
     }
diff --git a/posthog-core/test/posthog.featureflags.spec.ts b/posthog-core/test/posthog.featureflags.spec.ts
index f8a15d22..194644c7 100644
--- a/posthog-core/test/posthog.featureflags.spec.ts
+++ b/posthog-core/test/posthog.featureflags.spec.ts
@@ -586,4 +586,68 @@ describe('PostHog Core', () => {
       })
     })
   })
+
+  describe('bootstapped do not overwrite values', () => {
+    beforeEach(() => {
+      ;[posthog, mocks] = createTestClient(
+        'TEST_API_KEY',
+        {
+          flushAt: 1,
+          bootstrap: {
+            distinctId: 'tomato',
+            featureFlags: { 'bootstrap-1': 'variant-1', enabled: true, disabled: false },
+            featureFlagPayloads: {
+              'bootstrap-1': {
+                some: 'key',
+              },
+              enabled: 200,
+            },
+          },
+        },
+        (_mocks) => {
+          _mocks.fetch.mockImplementation((url) => {
+            if (url.includes('/decide/')) {
+              return Promise.resolve({
+                status: 200,
+                text: () => Promise.resolve('ok'),
+                json: () =>
+                  Promise.resolve({
+                    featureFlags: createMockFeatureFlags(),
+                    featureFlagPayloads: createMockFeatureFlagPayloads(),
+                  }),
+              })
+            }
+
+            return Promise.resolve({
+              status: 200,
+              text: () => Promise.resolve('ok'),
+              json: () =>
+                Promise.resolve({
+                  status: 'ok',
+                }),
+            })
+          })
+        },
+        {
+          distinct_id: '123',
+          feature_flags: { 'bootstrap-1': 'variant-2' },
+          feature_flag_payloads: { 'bootstrap-1': { some: 'other-key' } },
+        }
+      )
+    })
+
+    it('distinct id should not be overwritten if already there', () => {
+      expect(posthog.getDistinctId()).toEqual('123')
+    })
+
+    it('flags should not be overwritten if already there', () => {
+      expect(posthog.getFeatureFlag('bootstrap-1')).toEqual('variant-2')
+    })
+
+    it('flag payloads should not be overwritten if already there', () => {
+      expect(posthog.getFeatureFlagPayload('bootstrap-1')).toEqual({
+        some: 'other-key',
+      })
+    })
+  })
 })
diff --git a/posthog-core/test/test-utils/PostHogCoreTestClient.ts b/posthog-core/test/test-utils/PostHogCoreTestClient.ts
index 0a4451a6..5039e650 100644
--- a/posthog-core/test/test-utils/PostHogCoreTestClient.ts
+++ b/posthog-core/test/test-utils/PostHogCoreTestClient.ts
@@ -1,4 +1,4 @@
-import { PostHogCore, PostHogCoreOptions, PostHogFetchOptions, PostHogFetchResponse } from '../../src'
+import { JsonType, PostHogCore, PostHogCoreOptions, PostHogFetchOptions, PostHogFetchResponse } from '../../src'
 
 const version = '2.0.0-alpha'
 
@@ -42,9 +42,9 @@ export class PostHogCoreTestClient extends PostHogCore {
 export const createTestClient = (
   apiKey: string,
   options?: PostHogCoreOptions,
-  setupMocks?: (mocks: PostHogCoreTestClientMocks) => void
+  setupMocks?: (mocks: PostHogCoreTestClientMocks) => void,
+  storageCache: { [key: string]: string | JsonType } = {}
 ): [PostHogCoreTestClient, PostHogCoreTestClientMocks] => {
-  const storageCache: { [key: string]: string | undefined } = {}
   const mocks = {
     fetch: jest.fn<Promise<PostHogFetchResponse>, [string, PostHogFetchOptions]>(),
     storage: {