diff --git a/feature/registration/src/main/java/org/signal/registration/screens/pincreation/PinCreationScreen.kt b/feature/registration/src/main/java/org/signal/registration/screens/pincreation/PinCreationScreen.kt
index 65582bf61d..d0596211bb 100644
--- a/feature/registration/src/main/java/org/signal/registration/screens/pincreation/PinCreationScreen.kt
+++ b/feature/registration/src/main/java/org/signal/registration/screens/pincreation/PinCreationScreen.kt
@@ -401,7 +401,8 @@ private fun PinInputSection(
       isConfirm = isConfirm,
       isAlphanumericKeyboard = state.isAlphanumericKeyboard,
       isMismatch = state.pinMismatch,
-      matchesVerificationCode = state.pinMatchesVerificationCode
+      matchesVerificationCode = state.pinMatchesVerificationCode,
+      isTooWeak = state.pinTooWeak
     )
     Spacer(modifier = Modifier.height(16.dp))
     KeyboardToggleButton(
@@ -445,14 +446,16 @@ private fun PinInputLabel(
   isAlphanumericKeyboard: Boolean,
   isMismatch: Boolean,
   matchesVerificationCode: Boolean,
+  isTooWeak: Boolean,
   modifier: Modifier = Modifier
 ) {
-  val isError = !isConfirm && (isMismatch || matchesVerificationCode)
+  val isError = !isConfirm && (isMismatch || matchesVerificationCode || isTooWeak)
 
   Text(
     text = when {
       isConfirm -> stringResource(R.string.PinCreationScreen__reenter_pin)
       matchesVerificationCode -> stringResource(R.string.PinCreationScreen__reentered_verification_code)
+      isTooWeak -> stringResource(R.string.PinCreationScreen__choose_a_stronger_pin)
       isMismatch -> stringResource(R.string.PinCreationScreen__pins_dont_match)
       isAlphanumericKeyboard -> stringResource(R.string.PinCreationScreen__pin_at_least_4_characters)
       else -> stringResource(R.string.PinCreationScreen__pin_at_least_4_digits)
diff --git a/feature/registration/src/main/java/org/signal/registration/screens/pincreation/PinCreationState.kt b/feature/registration/src/main/java/org/signal/registration/screens/pincreation/PinCreationState.kt
index ba0e8152a4..6279e6dcc3 100644
--- a/feature/registration/src/main/java/org/signal/registration/screens/pincreation/PinCreationState.kt
+++ b/feature/registration/src/main/java/org/signal/registration/screens/pincreation/PinCreationState.kt
@@ -14,6 +14,7 @@ data class PinCreationState(
   val isConfirmEnabled: Boolean = false,
   val pinMismatch: Boolean = false,
   val pinMatchesVerificationCode: Boolean = false,
+  val pinTooWeak: Boolean = false,
   val loading: Boolean = false,
   val firstPin: String? = null,
   val submittedVerificationCode: String? = null,
@@ -21,7 +22,7 @@ data class PinCreationState(
   val dialogs: Dialogs = Dialogs()
 ) {
   override fun toString(): String {
-    return "PinCreationState(isAlphanumericKeyboard=$isAlphanumericKeyboard, isConfirmEnabled=$isConfirmEnabled, pinMismatch=$pinMismatch, pinMatchesVerificationCode=$pinMatchesVerificationCode, loading=$loading, firstPin=${firstPin?.let { "${it.length} chars" }}, submittedVerificationCode=${submittedVerificationCode?.censor()}, accountEntropyPool=${accountEntropyPool?.displayValue?.censor()}, dialogs=$dialogs)"
+    return "PinCreationState(isAlphanumericKeyboard=$isAlphanumericKeyboard, isConfirmEnabled=$isConfirmEnabled, pinMismatch=$pinMismatch, pinMatchesVerificationCode=$pinMatchesVerificationCode, pinTooWeak=$pinTooWeak, loading=$loading, firstPin=${firstPin?.let { "${it.length} chars" }}, submittedVerificationCode=${submittedVerificationCode?.censor()}, accountEntropyPool=${accountEntropyPool?.displayValue?.censor()}, dialogs=$dialogs)"
   }
 
   data class Dialogs(
diff --git a/feature/registration/src/main/java/org/signal/registration/screens/pincreation/PinCreationViewModel.kt b/feature/registration/src/main/java/org/signal/registration/screens/pincreation/PinCreationViewModel.kt
index 58e05087b4..01781a4124 100644
--- a/feature/registration/src/main/java/org/signal/registration/screens/pincreation/PinCreationViewModel.kt
+++ b/feature/registration/src/main/java/org/signal/registration/screens/pincreation/PinCreationViewModel.kt
@@ -22,6 +22,7 @@ import org.signal.registration.RegistrationFlowEvent
 import org.signal.registration.RegistrationFlowState
 import org.signal.registration.RegistrationRepository
 import org.signal.registration.RestoreDecision
+import org.whispersystems.signalservice.api.kbs.PinValidityChecker
 import kotlin.time.toKotlinDuration
 
 /**
@@ -66,12 +67,17 @@ class PinCreationViewModel(
         when {
           !state.isConfirmEnabled && event.pin == state.submittedVerificationCode -> {
             Log.w(TAG, "[PinSubmitted] User entered their verification code as their PIN. Prompting them to choose a different PIN.")
-            _state.value = state.copy(pinMatchesVerificationCode = true, pinMismatch = false)
+            _state.value = state.copy(pinMatchesVerificationCode = true, pinMismatch = false, pinTooWeak = false)
+          }
+
+          !state.isConfirmEnabled && !PinValidityChecker.valid(event.pin) -> {
+            Log.w(TAG, "[PinSubmitted] User entered a PIN that is too common. Prompting them to choose a stronger PIN.")
+            _state.value = state.copy(pinTooWeak = true, pinMismatch = false, pinMatchesVerificationCode = false)
           }
 
           !state.isConfirmEnabled -> {
             Log.d(TAG, "[PinSubmitted] First PIN entered. Asking the user to confirm it.")
-            _state.value = state.copy(firstPin = event.pin, isConfirmEnabled = true, pinMismatch = false, pinMatchesVerificationCode = false)
+            _state.value = state.copy(firstPin = event.pin, isConfirmEnabled = true, pinMismatch = false, pinMatchesVerificationCode = false, pinTooWeak = false)
           }
 
           event.pin != state.firstPin -> {
diff --git a/feature/registration/src/main/res/values/strings.xml b/feature/registration/src/main/res/values/strings.xml
index 4219c48937..9cea5c7ba6 100644
--- a/feature/registration/src/main/res/values/strings.xml
+++ b/feature/registration/src/main/res/values/strings.xml
@@ -377,6 +377,8 @@
     <string name="PinCreationScreen__reenter_pin">Re-enter PIN</string>
     <!-- Error shown below the PIN field when the confirmation PIN does not match the one the user first entered. -->
     <string name="PinCreationScreen__pins_dont_match">PINs don\'t match. Try again.</string>
+    <!-- Error shown below the PIN field when the user tries to create a PIN that is too easy to guess, such as one made of sequential or repeated digits. -->
+    <string name="PinCreationScreen__choose_a_stronger_pin">Choose a stronger PIN</string>
     <!-- Error shown below the PIN field when the user tries to create a PIN that matches the code used to verify their phone number. -->
     <string name="PinCreationScreen__reentered_verification_code">You re-entered the code that was already used to verify your phone number. Choose a new and unique Signal PIN.</string>
     <!-- Overflow menu item that opens a help article about Signal PINs. -->
diff --git a/feature/registration/src/test/java/org/signal/registration/screens/pincreation/PinCreationScreenTest.kt b/feature/registration/src/test/java/org/signal/registration/screens/pincreation/PinCreationScreenTest.kt
index 9a629c0530..234781d01a 100644
--- a/feature/registration/src/test/java/org/signal/registration/screens/pincreation/PinCreationScreenTest.kt
+++ b/feature/registration/src/test/java/org/signal/registration/screens/pincreation/PinCreationScreenTest.kt
@@ -10,6 +10,7 @@ import androidx.compose.ui.test.assertIsDisplayed
 import androidx.compose.ui.test.assertIsNotEnabled
 import androidx.compose.ui.test.junit4.createComposeRule
 import androidx.compose.ui.test.onNodeWithTag
+import androidx.compose.ui.test.onNodeWithText
 import androidx.compose.ui.test.performClick
 import androidx.compose.ui.test.performTextInput
 import androidx.test.core.app.ApplicationProvider
@@ -20,6 +21,7 @@ import org.robolectric.RobolectricTestRunner
 import org.robolectric.annotation.Config
 import org.signal.core.ui.CoreUiDependenciesRule
 import org.signal.core.ui.compose.theme.SignalTheme
+import org.signal.registration.R
 import org.signal.registration.test.TestTags
 
 /**
@@ -101,4 +103,19 @@ class PinCreationScreenTest {
 
     assert(emittedEvent is PinCreationScreenEvents.PinSubmitted)
   }
+
+  @Test
+  fun `when the pin is too weak, the stronger pin error is displayed`() {
+    composeTestRule.setContent {
+      SignalTheme {
+        PinCreationScreen(
+          state = PinCreationState(pinTooWeak = true),
+          onEvent = {}
+        )
+      }
+    }
+
+    val context = ApplicationProvider.getApplicationContext<Application>()
+    composeTestRule.onNodeWithText(context.getString(R.string.PinCreationScreen__choose_a_stronger_pin)).assertIsDisplayed()
+  }
 }
diff --git a/feature/registration/src/test/java/org/signal/registration/screens/pincreation/PinCreationViewModelTest.kt b/feature/registration/src/test/java/org/signal/registration/screens/pincreation/PinCreationViewModelTest.kt
index 6737127fdb..fdbbaf6240 100644
--- a/feature/registration/src/test/java/org/signal/registration/screens/pincreation/PinCreationViewModelTest.kt
+++ b/feature/registration/src/test/java/org/signal/registration/screens/pincreation/PinCreationViewModelTest.kt
@@ -82,7 +82,7 @@ class PinCreationViewModelTest {
     val states = collectStates()
     val initialState = PinCreationState(accountEntropyPool = AccountEntropyPool.generate())
 
-    viewModel.applyEvent(initialState, PinCreationScreenEvents.PinSubmitted("123456"))
+    viewModel.applyEvent(initialState, PinCreationScreenEvents.PinSubmitted("148502"))
 
     coVerify(exactly = 0) { mockRepository.setNewlyCreatedPin(any(), any(), any<MasterKey>()) }
     assertThat(emittedParentEvents).hasSize(0)
@@ -142,12 +142,107 @@ class PinCreationViewModelTest {
     val states = collectStates()
     val initialState = PinCreationState(accountEntropyPool = AccountEntropyPool.generate(), submittedVerificationCode = "123456")
 
-    viewModel.applyEvent(initialState, PinCreationScreenEvents.PinSubmitted("987654"))
+    viewModel.applyEvent(initialState, PinCreationScreenEvents.PinSubmitted("148502"))
 
     assertThat(states.last().isConfirmEnabled).isTrue()
     assertThat(states.last().pinMatchesVerificationCode).isFalse()
   }
 
+  // ==================== Weak PIN Tests ====================
+
+  @Test
+  fun `first PinSubmitted with an ascending sequential PIN is rejected as too weak`() = runTest(testDispatcher) {
+    val states = collectStates()
+    val initialState = PinCreationState(accountEntropyPool = AccountEntropyPool.generate())
+
+    viewModel.applyEvent(initialState, PinCreationScreenEvents.PinSubmitted("1234"))
+
+    coVerify(exactly = 0) { mockRepository.setNewlyCreatedPin(any(), any(), any<MasterKey>()) }
+    assertThat(emittedParentEvents).hasSize(0)
+    assertThat(states.last().pinTooWeak).isTrue()
+    assertThat(states.last().isConfirmEnabled).isFalse()
+    assertThat(states.last().firstPin).isNull()
+  }
+
+  @Test
+  fun `first PinSubmitted with a descending sequential PIN is rejected as too weak`() = runTest(testDispatcher) {
+    val states = collectStates()
+    val initialState = PinCreationState(accountEntropyPool = AccountEntropyPool.generate())
+
+    viewModel.applyEvent(initialState, PinCreationScreenEvents.PinSubmitted("43210"))
+
+    assertThat(states.last().pinTooWeak).isTrue()
+    assertThat(states.last().isConfirmEnabled).isFalse()
+  }
+
+  @Test
+  fun `first PinSubmitted with a repeated-digit PIN is rejected as too weak`() = runTest(testDispatcher) {
+    val states = collectStates()
+    val initialState = PinCreationState(accountEntropyPool = AccountEntropyPool.generate())
+
+    viewModel.applyEvent(initialState, PinCreationScreenEvents.PinSubmitted("9999"))
+
+    assertThat(states.last().pinTooWeak).isTrue()
+    assertThat(states.last().isConfirmEnabled).isFalse()
+  }
+
+  @Test
+  fun `first PinSubmitted with a sequential non-arabic-numeral PIN is rejected as too weak`() = runTest(testDispatcher) {
+    val states = collectStates()
+    val initialState = PinCreationState(accountEntropyPool = AccountEntropyPool.generate())
+
+    viewModel.applyEvent(initialState, PinCreationScreenEvents.PinSubmitted("١٢٣٤٥"))
+
+    assertThat(states.last().pinTooWeak).isTrue()
+    assertThat(states.last().isConfirmEnabled).isFalse()
+  }
+
+  @Test
+  fun `first PinSubmitted with a sequential alphanumeric PIN is allowed`() = runTest(testDispatcher) {
+    val states = collectStates()
+    val initialState = PinCreationState(accountEntropyPool = AccountEntropyPool.generate(), isAlphanumericKeyboard = true)
+
+    viewModel.applyEvent(initialState, PinCreationScreenEvents.PinSubmitted("abcd"))
+
+    assertThat(states.last().pinTooWeak).isFalse()
+    assertThat(states.last().isConfirmEnabled).isTrue()
+  }
+
+  @Test
+  fun `first PinSubmitted matching the verification code is reported as such rather than as too weak`() = runTest(testDispatcher) {
+    val states = collectStates()
+    val initialState = PinCreationState(accountEntropyPool = AccountEntropyPool.generate(), submittedVerificationCode = "123456")
+
+    viewModel.applyEvent(initialState, PinCreationScreenEvents.PinSubmitted("123456"))
+
+    assertThat(states.last().pinMatchesVerificationCode).isTrue()
+    assertThat(states.last().pinTooWeak).isFalse()
+  }
+
+  @Test
+  fun `first PinSubmitted with a strong PIN clears a previous too-weak error`() = runTest(testDispatcher) {
+    val states = collectStates()
+    val weakState = PinCreationState(accountEntropyPool = AccountEntropyPool.generate(), pinTooWeak = true)
+
+    viewModel.applyEvent(weakState, PinCreationScreenEvents.PinSubmitted("148502"))
+
+    assertThat(states.last().pinTooWeak).isFalse()
+    assertThat(states.last().isConfirmEnabled).isTrue()
+  }
+
+  @Test
+  fun `weak PIN check is skipped on the confirmation step`() = runTest(testDispatcher) {
+    val aep = AccountEntropyPool.generate()
+    val confirmState = PinCreationState(accountEntropyPool = aep, isConfirmEnabled = true, firstPin = "148502")
+
+    coEvery { mockRepository.setNewlyCreatedPin(any(), any(), any<MasterKey>()) } returns RequestResult.Success(null)
+
+    viewModel.applyEvent(confirmState, PinCreationScreenEvents.PinSubmitted("148502"))
+
+    coVerify { mockRepository.setNewlyCreatedPin("148502", any(), any<MasterKey>()) }
+    assertThat(emittedParentEvents).contains(RegistrationFlowEvent.RegistrationComplete)
+  }
+
   // ==================== PinSubmitted Success Tests ====================
 
   @Test