diff --git a/src/AzureIoTHub.Portal.Server.Tests.Unit/Controllers/v1.0/DevicesControllerTests.cs b/src/AzureIoTHub.Portal.Server.Tests.Unit/Controllers/v1.0/DevicesControllerTests.cs
index 03f47d285..6e1cc2fc1 100644
--- a/src/AzureIoTHub.Portal.Server.Tests.Unit/Controllers/v1.0/DevicesControllerTests.cs
+++ b/src/AzureIoTHub.Portal.Server.Tests.Unit/Controllers/v1.0/DevicesControllerTests.cs
@@ -191,6 +191,9 @@ public async Task CreateDeviceAsyncStateUnderTestExpectedBehavior()
 
             Twin twin = null;
 
+            _ = this.mockDeviceService.Setup(c => c.GetDevice(It.IsAny<string>()))
+                .ReturnsAsync((Device)null);
+
             _ = this.mockDeviceTwinMapper.Setup(c => c.UpdateTwin(It.Is<Twin>(x => x.DeviceId == device.DeviceID), It.Is<DeviceDetails>(x => x == device)))
                 .Callback<Twin, DeviceDetails>((t, _) => twin = t);
 
@@ -782,5 +785,26 @@ public async Task WhenPropertyNotInModelSetPropertiesShouldNotUpdateDesiredPrope
 
             this.mockRepository.VerifyAll();
         }
+
+        [Test]
+        public async Task CreateDeviceAsyncDuplicatedDeviceIdShouldThrowInternalServerErrorException()
+        {
+            // Arrange
+            var devicesController = CreateDevicesController();
+
+            _ = this.mockDeviceService.Setup(c => c.GetDevice(It.IsAny<string>()))
+                .ReturnsAsync(new Device());
+
+            // Act
+            //var result = await existingDevice.GetItem(deviceID);
+            var result = async () => await devicesController.CreateDeviceAsync(new DeviceDetails());
+
+            // Assert
+            //Assert.IsNotNull(result);
+            //Assert.IsAssignableFrom<OkResult>(result);
+            _ = await result.Should().ThrowAsync<InternalServerErrorException>();
+            this.mockRepository.VerifyAll();
+        }
+
     }
 }
diff --git a/src/AzureIoTHub.Portal.Server.Tests.Unit/Controllers/v1.0/LoRaWAN/LoRaWANDevicesControllerTests.cs b/src/AzureIoTHub.Portal.Server.Tests.Unit/Controllers/v1.0/LoRaWAN/LoRaWANDevicesControllerTests.cs
index 4237f61d8..5457d6491 100644
--- a/src/AzureIoTHub.Portal.Server.Tests.Unit/Controllers/v1.0/LoRaWAN/LoRaWANDevicesControllerTests.cs
+++ b/src/AzureIoTHub.Portal.Server.Tests.Unit/Controllers/v1.0/LoRaWAN/LoRaWANDevicesControllerTests.cs
@@ -396,6 +396,9 @@ public async Task CreateDeviceAsyncStateUnderTestExpectedBehavior()
 
             Twin twin = null;
 
+            _ = this.mockDeviceService.Setup(c => c.GetDevice(It.IsAny<string>()))
+                .ReturnsAsync((Device)null);
+
             _ = this.mockDeviceTwinMapper.Setup(c => c.UpdateTwin(It.Is<Twin>(x => x.DeviceId == device.DeviceID), It.Is<LoRaDeviceDetails>(x => x == device)))
                 .Callback<Twin, LoRaDeviceDetails>((t, _) => twin = t);
 
diff --git a/src/AzureIoTHub.Portal/Server/Controllers/v1.0/DevicesControllerBase.cs b/src/AzureIoTHub.Portal/Server/Controllers/v1.0/DevicesControllerBase.cs
index f8151a615..247ae155e 100644
--- a/src/AzureIoTHub.Portal/Server/Controllers/v1.0/DevicesControllerBase.cs
+++ b/src/AzureIoTHub.Portal/Server/Controllers/v1.0/DevicesControllerBase.cs
@@ -152,6 +152,12 @@ public virtual async Task<IActionResult> CreateDeviceAsync(TModel device)
                 throw new ProblemDetailsException(validation);
             }
 
+            var existingDevice = await this.devicesService.GetDevice(device.DeviceID);
+            if (existingDevice != null)
+            {
+                throw new InternalServerErrorException($"The device with ID {device.DeviceID} already exists");
+            }
+
             // Create a new Twin from the form's fields.
             var newTwin = new Twin()
             {