diff --git a/LiftLog.Lib/Services/AesEncryptionService.cs b/LiftLog.Lib/Services/AesEncryptionService.cs
index ed0b982f..951e275a 100644
--- a/LiftLog.Lib/Services/AesEncryptionService.cs
+++ b/LiftLog.Lib/Services/AesEncryptionService.cs
@@ -17,11 +17,22 @@ public ValueTask<byte[]> DecryptAsync(byte[] data, byte[] IV, byte[] key)
         return ValueTask.FromResult(decryptor.TransformFinalBlock(data, 0, data.Length));
     }
 
-    public ValueTask<(byte[] EncryptedPayload, byte[] IV)> EncryptAsync(byte[] data, byte[] key)
+    public ValueTask<(byte[] EncryptedPayload, byte[] IV)> EncryptAsync(
+        byte[] data,
+        byte[] key,
+        byte[]? iv = null
+    )
     {
         var aes = Aes.Create();
 
-        aes.GenerateIV();
+        if (iv is not null)
+        {
+            aes.IV = iv;
+        }
+        else
+        {
+            aes.GenerateIV();
+        }
         aes.Key = key;
 
         using var encryptor = aes.CreateEncryptor();
diff --git a/LiftLog.Lib/Services/IEncryptionService.cs b/LiftLog.Lib/Services/IEncryptionService.cs
index dcb33fa6..3932df98 100644
--- a/LiftLog.Lib/Services/IEncryptionService.cs
+++ b/LiftLog.Lib/Services/IEncryptionService.cs
@@ -4,6 +4,10 @@ public interface IEncryptionService
 {
     ValueTask<byte[]> DecryptAsync(byte[] data, byte[] IV, byte[] key);
 
-    public ValueTask<(byte[] EncryptedPayload, byte[] IV)> EncryptAsync(byte[] data, byte[] key);
+    public ValueTask<(byte[] EncryptedPayload, byte[] IV)> EncryptAsync(
+        byte[] data,
+        byte[] key,
+        byte[]? iv = null
+    );
     ValueTask<byte[]> GenerateKeyAsync();
 }
diff --git a/LiftLog.Tests/Encryption/AesEncryptionServiceTests.cs b/LiftLog.Tests/Encryption/AesEncryptionServiceTests.cs
index 99e0b780..e5b54ced 100644
--- a/LiftLog.Tests/Encryption/AesEncryptionServiceTests.cs
+++ b/LiftLog.Tests/Encryption/AesEncryptionServiceTests.cs
@@ -37,4 +37,24 @@ public async Task EncryptAndDecrypt_EncryptsAndDecryptsData()
         // Assert
         Assert.Equal(data, decryptedData);
     }
+
+    [Fact]
+    public async Task EncryptAndDecrypt_EncryptsAndDecryptsDataGivenSameIV()
+    {
+        // Arrange
+        var key = await _encryptionService.GenerateKeyAsync();
+        var data1 = Encoding.UTF8.GetBytes("Hello, world!");
+        var data2 = Encoding.UTF8.GetBytes("Goodbye, world!");
+
+        // Act
+        var (encryptedData1, iv) = await _encryptionService.EncryptAsync(data1, key);
+        var decryptedData1 = await _encryptionService.DecryptAsync(encryptedData1, iv, key);
+
+        var (encryptedData2, _) = await _encryptionService.EncryptAsync(data2, key, iv);
+        var decryptedData2 = await _encryptionService.DecryptAsync(encryptedData2, iv, key);
+
+        // Assert
+        Assert.Equal(data1, decryptedData1);
+        Assert.Equal(data2, decryptedData2);
+    }
 }
diff --git a/LiftLog.Web/Services/JsAesEncryptionService.cs b/LiftLog.Web/Services/JsAesEncryptionService.cs
index 70aece54..d1cc46b0 100644
--- a/LiftLog.Web/Services/JsAesEncryptionService.cs
+++ b/LiftLog.Web/Services/JsAesEncryptionService.cs
@@ -10,7 +10,11 @@ public ValueTask<byte[]> DecryptAsync(byte[] data, byte[] IV, byte[] key)
         throw new NotImplementedException();
     }
 
-    public ValueTask<(byte[] EncryptedPayload, byte[] IV)> EncryptAsync(byte[] data, byte[] key)
+    public ValueTask<(byte[] EncryptedPayload, byte[] IV)> EncryptAsync(
+        byte[] data,
+        byte[] key,
+        byte[]? iv = null
+    )
     {
         throw new NotImplementedException();
     }