diff --git a/feature/registration/src/main/java/org/signal/registration/screens/signallogincredentials/AccountIdFormat.kt b/feature/registration/src/main/java/org/signal/registration/screens/signallogincredentials/AccountIdFormat.kt
index e7f2cadded..c6a0230ca0 100644
--- a/feature/registration/src/main/java/org/signal/registration/screens/signallogincredentials/AccountIdFormat.kt
+++ b/feature/registration/src/main/java/org/signal/registration/screens/signallogincredentials/AccountIdFormat.kt
@@ -16,14 +16,17 @@ internal object AccountIdFormat {
   /** Offsets in a raw account ID that a dash is inserted in front of. */
   private val DASH_OFFSETS = intArrayOf(8, 12, 16, 20)
 
-  /** Rewrites a raw account ID with the dashes a UUID is normally written with. */
+  /**
+   * Rewrites a raw account ID with the dashes and uppercasing a UUID is normally written with.
+   */
   fun dashed(accountId: String): String {
     return buildString {
       for ((index, character) in accountId.withIndex()) {
         if (index in DASH_OFFSETS) {
           append('-')
         }
-        append(character)
+        // Uppercase on a per-character basis so as to not screw up offsets
+        append(character.uppercaseChar())
       }
     }
   }
diff --git a/feature/registration/src/main/java/org/signal/registration/screens/signallogincredentials/SignalLoginCredentialEntryScreen.kt b/feature/registration/src/main/java/org/signal/registration/screens/signallogincredentials/SignalLoginCredentialEntryScreen.kt
index b2e68a4477..ad5b5fc5ea 100644
--- a/feature/registration/src/main/java/org/signal/registration/screens/signallogincredentials/SignalLoginCredentialEntryScreen.kt
+++ b/feature/registration/src/main/java/org/signal/registration/screens/signallogincredentials/SignalLoginCredentialEntryScreen.kt
@@ -470,7 +470,7 @@ internal object AccountIdVisualTransformation : VisualTransformation {
 
   override fun filter(text: AnnotatedString): TransformedText {
     return TransformedText(
-      text = AnnotatedString(AccountIdFormat.dashed(text.text).uppercase()),
+      text = AnnotatedString(AccountIdFormat.dashed(text.text)),
       offsetMapping = AccountIdOffsetMapping(text.length)
     )
   }
diff --git a/feature/registration/src/test/java/org/signal/registration/screens/signallogincredentials/AccountIdVisualTransformationTest.kt b/feature/registration/src/test/java/org/signal/registration/screens/signallogincredentials/AccountIdVisualTransformationTest.kt
index 82ac0a539c..cef07fb3bb 100644
--- a/feature/registration/src/test/java/org/signal/registration/screens/signallogincredentials/AccountIdVisualTransformationTest.kt
+++ b/feature/registration/src/test/java/org/signal/registration/screens/signallogincredentials/AccountIdVisualTransformationTest.kt
@@ -15,6 +15,9 @@ class AccountIdVisualTransformationTest {
   companion object {
     private const val FULL_KEY = "a6b284822e3283d07f2391360a4c2b91"
     private const val FULL_KEY_FORMATTED = "A6B28482-2E32-83D0-7F23-91360A4C2B91"
+
+    /** Characters whose whole-string uppercase mapping is longer than the character itself. */
+    private val LENGTH_CHANGING_CHARACTERS = listOf('ß', 'ʼn', 'ff', 'fi', 'ǰ')
   }
 
   @Test
@@ -54,5 +57,33 @@ class AccountIdVisualTransformationTest {
     }
   }
 
+  @Test
+  fun `characters that uppercase into multiple characters stay one character long`() {
+    for (character in LENGTH_CHANGING_CHARACTERS) {
+      assertThat(transform(character.toString()).length).isEqualTo(1)
+      assertThat(transform("a6b2848$character")).isEqualTo("A6B2848${character.uppercaseChar()}")
+    }
+  }
+
+  @Test
+  fun `every cursor position round trips even when the key holds characters that normally expand`() {
+    for (character in LENGTH_CHANGING_CHARACTERS) {
+      val key = character + FULL_KEY.drop(1)
+      val mapping = AccountIdVisualTransformation.filter(AnnotatedString(key)).offsetMapping
+      val transformedLength = transform(key).length
+
+      for (offset in 0..key.length) {
+        val transformed = mapping.originalToTransformed(offset)
+
+        assertThat(transformed in 0..transformedLength).isEqualTo(true)
+        assertThat(mapping.transformedToOriginal(transformed)).isEqualTo(offset)
+      }
+
+      for (offset in 0..transformedLength) {
+        assertThat(mapping.transformedToOriginal(offset) in 0..key.length).isEqualTo(true)
+      }
+    }
+  }
+
   private fun transform(text: String): String = AccountIdVisualTransformation.filter(AnnotatedString(text)).text.text
 }