diff --git a/service/src/main/java/org/whispersystems/textsecuregcm/storage/Accounts.java b/service/src/main/java/org/whispersystems/textsecuregcm/storage/Accounts.java
index fab835349..2fbe8c46f 100644
--- a/service/src/main/java/org/whispersystems/textsecuregcm/storage/Accounts.java
+++ b/service/src/main/java/org/whispersystems/textsecuregcm/storage/Accounts.java
@@ -429,6 +429,24 @@ public class Accounts extends AbstractDynamoDbStore {
         succeeded = true;
       } catch (final JsonProcessingException e) {
         throw new IllegalArgumentException(e);
+      } catch (final TransactionCanceledException e) {
+        if (e.hasCancellationReasons() && e.cancellationReasons().size() == 6) {
+          // the cancellation reasons map to the write items:
+          // 0. phone number constraint delete - no conditions
+          // 1. phone number constraint put - conditional on the key not existing (it is deleted by 0)
+          // 2. pni constraint delete - no conditions
+          // 3. pni constraint put - conditional on the key not existing (it is deleted by 2)
+          // 4. deleted accounts delete - no conditions
+          // 5. account update - conditional on #version = :version
+          if (CONDITIONAL_CHECK_FAILED.equals(e.cancellationReasons().get(5).code())) {
+            // the #version = :version condition failed, which indicates a concurrent update
+            throw new ContestedOptimisticLockException();
+          }
+        } else {
+          log.warn("Unexpected cancellation reasons: {}", e.cancellationReasons());
+
+        }
+        throw e;
       } finally {
         if (!succeeded) {
           account.setNumber(originalNumber, originalPni);
diff --git a/service/src/test/java/org/whispersystems/textsecuregcm/storage/AccountsTest.java b/service/src/test/java/org/whispersystems/textsecuregcm/storage/AccountsTest.java
index 8ef8e1356..7cc18ea96 100644
--- a/service/src/test/java/org/whispersystems/textsecuregcm/storage/AccountsTest.java
+++ b/service/src/test/java/org/whispersystems/textsecuregcm/storage/AccountsTest.java
@@ -885,6 +885,41 @@ class AccountsTest {
     assertThrows(TransactionCanceledException.class, () -> accounts.changeNumber(account, targetNumber, existingPhoneNumberIdentifier, Optional.empty(), Collections.emptyList()));
   }
 
+  @Test
+  public void testChangeNumberContestedOptimisticLock() {
+    final String originalNumber = "+14151112222";
+    final String targetNumber = "+14151113333";
+
+    final UUID originalPni = UUID.randomUUID();
+    final UUID targetPni = UUID.randomUUID();
+
+    final Device device = generateDevice(DEVICE_ID_1);
+    final Account firstAccountInstance = generateAccount(originalNumber, UUID.randomUUID(), originalPni,
+        List.of(device));
+
+    createAccount(firstAccountInstance);
+
+    final Account secondAccountInstance = accounts.getByAccountIdentifier(firstAccountInstance.getUuid()).orElseThrow();
+
+    // update via the first instance, which will update the version
+    firstAccountInstance.setCurrentProfileVersion("1");
+    accounts.update(firstAccountInstance);
+
+    assertThrows(ContestedOptimisticLockException.class,
+        () -> accounts.changeNumber(secondAccountInstance, targetNumber, targetPni, Optional.empty(),
+            Collections.emptyList()), "Second account instance has stale version");
+
+    final Account refreshedAccountInstance = accounts.getByAccountIdentifier(firstAccountInstance.getUuid())
+        .orElseThrow();
+    accounts.changeNumber(refreshedAccountInstance, targetNumber, targetPni, Optional.empty(),
+        Collections.emptyList());
+
+    assertPhoneNumberConstraintDoesNotExist(originalNumber);
+    assertPhoneNumberIdentifierConstraintDoesNotExist(originalPni);
+    assertPhoneNumberConstraintExists(targetNumber, firstAccountInstance.getUuid());
+    assertPhoneNumberIdentifierConstraintExists(targetPni, firstAccountInstance.getUuid());
+  }
+
   @Test
   void testSwitchUsernameHashes() {
     final Account account = generateAccount("+18005551234", UUID.randomUUID(), UUID.randomUUID());