diff --git a/app/src/main/java/org/thoughtcrime/securesms/registration/v2/AppRegistrationStorageController.kt b/app/src/main/java/org/thoughtcrime/securesms/registration/v2/AppRegistrationStorageController.kt
index 3b988d31da..f8d0238b7c 100644
--- a/app/src/main/java/org/thoughtcrime/securesms/registration/v2/AppRegistrationStorageController.kt
+++ b/app/src/main/java/org/thoughtcrime/securesms/registration/v2/AppRegistrationStorageController.kt
@@ -750,6 +750,11 @@ class AppRegistrationStorageController(private val context: Context) : StorageCo
     val e164 = accountData.e164?.nullIfBlank()
     val isAciChanged = SignalStore.account.aci != aci
 
+    if (isAciChanged && SignalStore.registration.isRegistrationComplete) {
+      Log.i(TAG, "[applyAccountData] Registering a different account than the one this device completed registration for. Clearing registration-complete so the post-registration steps run again.")
+      SignalStore.registration.clearRegistrationComplete()
+    }
+
     if (pni == null) {
       Log.i(TAG, "[applyAccountData] No PNI in the account data. Registering an account with no phone number. Clearing any E164/PNI state from a previous registration.")
       SignalStore.account.clearE164AndPni()
diff --git a/app/src/test/java/org/thoughtcrime/securesms/registration/v2/AppRegistrationStorageControllerTest.kt b/app/src/test/java/org/thoughtcrime/securesms/registration/v2/AppRegistrationStorageControllerTest.kt
index 7b303c16e6..bf1035c3f3 100644
--- a/app/src/test/java/org/thoughtcrime/securesms/registration/v2/AppRegistrationStorageControllerTest.kt
+++ b/app/src/test/java/org/thoughtcrime/securesms/registration/v2/AppRegistrationStorageControllerTest.kt
@@ -295,6 +295,51 @@ class AppRegistrationStorageControllerTest {
     assertThat(SignalStore.account.isRegistered).isTrue()
   }
 
+  @Test
+  fun `commit - different account than a completed registration - clears registration complete`() = runBlocking<Unit> {
+    SignalStore.account.setAci(ACI.from(UUID.randomUUID()))
+    SignalStore.account.setRegistered(true)
+    SignalStore.registration.markRegistrationComplete()
+
+    seedInProgressData(
+      RegistrationData(
+        accountData = accountData().newBuilder()
+          .e164("")
+          .pni("")
+          .pniIdentityKeyPair(ByteString.EMPTY)
+          .pniSignedPreKey(ByteString.EMPTY)
+          .pniLastResortKyberPreKey(ByteString.EMPTY)
+          .pniRegistrationId(0)
+          .build(),
+        accountEntropyPool = aep.value
+      )
+    )
+
+    controller.commitRegistrationData()
+
+    assertThat(SignalStore.account.aci).isEqualTo(aci)
+    assertThat(SignalStore.registration.isRegistrationComplete).isFalse()
+  }
+
+  @Test
+  fun `commit - same account as a completed registration - leaves registration complete`() = runBlocking<Unit> {
+    SignalStore.account.setAci(aci)
+    SignalStore.account.setRegistered(true)
+    SignalStore.registration.markRegistrationComplete()
+
+    seedInProgressData(
+      RegistrationData(
+        accountData = accountData(reRegistration = true),
+        accountEntropyPool = aep.value,
+        pin = PIN
+      )
+    )
+
+    controller.commitRegistrationData()
+
+    assertThat(SignalStore.registration.isRegistrationComplete).isTrue()
+  }
+
   @Test
   fun `commit - pin opted out - applies svr opt out`() = runBlocking<Unit> {
     seedInProgressData(
diff --git a/feature/registration/src/test/java/org/signal/registration/RegistrationEndToEndTest.kt b/feature/registration/src/test/java/org/signal/registration/RegistrationEndToEndTest.kt
index dedc060688..b21e799a17 100644
--- a/feature/registration/src/test/java/org/signal/registration/RegistrationEndToEndTest.kt
+++ b/feature/registration/src/test/java/org/signal/registration/RegistrationEndToEndTest.kt
@@ -1701,6 +1701,42 @@ class RegistrationEndToEndTest {
     assert(request.pniPreKeys == null) { "An account with no phone number has no PNI, so no PNI key material should be sent" }
   }
 
+  @Test
+  fun `registering a new signal login on a device already registered to another account commits a different aci`() {
+    enableSignalLoginRegistration()
+    val preExisting = preExistingRegistrationData(E164)
+    storageController.preExistingRegistrationData = preExisting
+
+    var registrationComplete = false
+    launchRegistrationFlow(onRegistrationComplete = { registrationComplete = true })
+
+    startSignalLoginRegistration()
+    buySignalLogin()
+
+    waitForTag(TestTags.SIGNAL_LOGIN_INFO_SCREEN)
+    val login = registeredSignalLogin()
+
+    recordSignalLoginManually()
+    enterSignalLogin(login)
+
+    waitForTag(TestTags.ADD_USERNAME_FIELD)
+    composeTestRule.onNodeWithTag(TestTags.ADD_USERNAME_FIELD).performTextInput(USERNAME)
+    waitForEnabledTag(TestTags.ADD_USERNAME_NEXT_BUTTON)
+    composeTestRule.onNodeWithTag(TestTags.ADD_USERNAME_NEXT_BUTTON).performClick()
+
+    waitFor("registration to complete") { registrationComplete }
+
+    // The app detects the switch to a new account by comparing the committed ACI against the device's, and uses it to
+    // re-run the post-registration steps (like setting a profile name) that the previous account already completed.
+    val accountData = storageController.committedData?.accountData
+    assert(accountData != null) { "Expected account data to be committed" }
+    assert(accountData!!.aci == login.aci.toString()) { "Expected committed ACI ${login.aci} but was ${accountData.aci}" }
+    assert(accountData.aci != preExisting.aci.toString()) { "Expected a new account, but the committed ACI is the one already on the device" }
+    assert(!accountData.reRegistration) { "Expected a brand new account to not be flagged as a re-registration" }
+    assert(networkController.lastRegisterAccountRequest?.aci == null) { "Expected the device's existing ACI to not be sent but was ${networkController.lastRegisterAccountRequest?.aci}" }
+    assert(storageController.savedUsername == "$USERNAME.42") { "Expected the confirmed username to be saved but was ${storageController.savedUsername}" }
+  }
+
   @Test
   fun `a purchased signal login that the password manager takes and hands back moves the user on to the username step`() {
     enableSignalLoginRegistration()