diff --git a/data/address-book/src/main/kotlin/com/tangem/data/addressbook/DefaultAddressBookRepository.kt b/data/address-book/src/main/kotlin/com/tangem/data/addressbook/DefaultAddressBookRepository.kt
index 2fbb2ee921..030d7cabdf 100644
--- a/data/address-book/src/main/kotlin/com/tangem/data/addressbook/DefaultAddressBookRepository.kt
+++ b/data/address-book/src/main/kotlin/com/tangem/data/addressbook/DefaultAddressBookRepository.kt
@@ -102,9 +102,10 @@ internal class DefaultAddressBookRepository(
             writeMutex.withLock {
                 val userWallet = findUserWallet(contact.walletId.stringValue)
                     ?: return@withLock AddressBookSyncError.Unknown.left()
-                val current = currentContacts(contact.walletId, userWallet)
-                val merged = current.filterNot { it.id == contact.id } + contact
-                persist(userWallet, AddressBook(contacts = merged))
+                currentContacts(contact.walletId, userWallet).flatMap { current ->
+                    val merged = current.filterNot { it.id == contact.id } + contact
+                    persist(userWallet, AddressBook(contacts = merged))
+                }
             }
         }
 
@@ -183,9 +184,28 @@ internal class DefaultAddressBookRepository(
         )
     }
 
-    private suspend fun currentContacts(userWalletId: UserWalletId, userWallet: UserWallet): List<Contact> {
-        val blob = blobStore.getBlobSync(userWalletId) ?: return emptyList()
-        return decryptContacts(blob, userWallet)
+    /**
+     * The contacts currently stored for [userWalletId], as the base a write is merged onto.
+     *
+     * A missing blob means no book exists yet → an empty base, so the first contact legitimately creates it.
+     * But a blob that fails to decrypt must surface as [AddressBookSyncError.DecryptionFailed] rather than an empty
+     * list: treating a broken book as empty would let a merged write overwrite the (non-empty) backend copy with a
+     * book built from a single new contact, wiping every existing one.
+     */
+    private suspend fun currentContacts(
+        userWalletId: UserWalletId,
+        userWallet: UserWallet,
+    ): Either<AddressBookSyncError, List<Contact>> {
+        val blob = blobStore.getBlobSync(userWalletId) ?: return emptyList<Contact>().right()
+        return cipher.decrypt(blob, userWallet)
+            .map { it.contacts }
+            .mapLeft { error ->
+                logger.e(
+                    "Refusing to overwrite address book for wallet $userWalletId: it is stored but decrypt " +
+                        "failed with $error",
+                )
+                AddressBookSyncError.DecryptionFailed
+            }
     }
 
     /**
diff --git a/data/address-book/src/test/kotlin/com/tangem/data/addressbook/DefaultAddressBookRepositoryTest.kt b/data/address-book/src/test/kotlin/com/tangem/data/addressbook/DefaultAddressBookRepositoryTest.kt
index 079d762fe6..1504c70544 100644
--- a/data/address-book/src/test/kotlin/com/tangem/data/addressbook/DefaultAddressBookRepositoryTest.kt
+++ b/data/address-book/src/test/kotlin/com/tangem/data/addressbook/DefaultAddressBookRepositoryTest.kt
@@ -288,6 +288,25 @@ internal class DefaultAddressBookRepositoryTest {
         coVerify(exactly = 0) { blobStore.storeBlob(any()) }
     }
 
+    @Test
+    fun `GIVEN stored book that fails to decrypt WHEN saveContact THEN returns DecryptionFailed and pushes nothing`() =
+        runTest {
+            // Arrange
+            val storedBlob = createBlob()
+            coEvery { blobStore.getBlobSync(UserWalletId(WALLET_A)) } returns storedBlob
+            every { cipher.decrypt(storedBlob, userWallet) } returns AddressBookCryptoError.DecryptionFailed.left()
+
+            // Act
+            val result = repository.saveContact(createContact(id = "c2", name = "Bob"))
+
+            // Assert
+            assertThat(result).isEqualTo(AddressBookSyncError.DecryptionFailed.left())
+            // The broken book is left untouched: nothing is encrypted, pushed, or stored.
+            coVerify(exactly = 0) { addressBookApi.updateAddressBook(any(), any(), any()) }
+            coVerify(exactly = 0) { blobStore.storeBlob(any()) }
+            coVerify(exactly = 0) { eTagsStore.store(any(), any(), any()) }
+        }
+
     @Test
     fun `GIVEN existing contact id WHEN saveContact THEN replaces it`() = runTest {
         // Arrange
diff --git a/domain/address-book/src/main/kotlin/com/tangem/domain/addressbook/error/AddressBookSyncError.kt b/domain/address-book/src/main/kotlin/com/tangem/domain/addressbook/error/AddressBookSyncError.kt
index 86b76d1a15..1e01d618cb 100644
--- a/domain/address-book/src/main/kotlin/com/tangem/domain/addressbook/error/AddressBookSyncError.kt
+++ b/domain/address-book/src/main/kotlin/com/tangem/domain/addressbook/error/AddressBookSyncError.kt
@@ -22,6 +22,13 @@ sealed interface AddressBookSyncError {
     /** No network or the request could not be completed. */
     data object Network : AddressBookSyncError
 
+    /**
+     * The wallet already has a stored book that could not be decrypted. The write is refused so the broken
+     * (but non-empty) backend book is not overwritten by a fresh one built on the device — see
+     * [com.tangem.domain.addressbook.repository.AddressBookRepository.saveContact].
+     */
+    data object DecryptionFailed : AddressBookSyncError
+
     /** Any other unexpected failure (encryption, missing data, unmapped HTTP code). */
     data object Unknown : AddressBookSyncError
 }
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