diff --git a/sql/001-nodes.sql b/sql/001-nodes.sql
new file mode 100644
index 0000000..dac8ae6
--- /dev/null
+++ b/sql/001-nodes.sql
@@ -0,0 +1,5 @@
+-- make device index unique
+
+DROP INDEX IF EXISTS public.i_nodes_type;
+
+CREATE UNIQUE INDEX IF NOT EXISTS i_nodes_device ON public.nodes (device);
diff --git a/sql/initial/004-nodes.sql b/sql/initial/004-nodes.sql
index 511926f..35724a1 100644
--- a/sql/initial/004-nodes.sql
+++ b/sql/initial/004-nodes.sql
@@ -19,7 +19,7 @@ ALTER TABLE IF EXISTS public.nodes
 -- Index: public.i_nodes_type
 -- DROP INDEX IF EXISTS public.i_nodes_type;
 
-CREATE INDEX IF NOT EXISTS i_nodes_device ON public.nodes (device);
+CREATE UNIQUE INDEX IF NOT EXISTS i_nodes_device ON public.nodes (device);
 
 
 -- Revoke all permissions from existing roles
diff --git a/src/integration-test/kotlin/ltd/hlaeja/controller/NodeEndpoint.kt b/src/integration-test/kotlin/ltd/hlaeja/controller/NodeEndpoint.kt
index 79da16b..e40dfff 100644
--- a/src/integration-test/kotlin/ltd/hlaeja/controller/NodeEndpoint.kt
+++ b/src/integration-test/kotlin/ltd/hlaeja/controller/NodeEndpoint.kt
@@ -9,6 +9,8 @@ import org.assertj.core.api.junit.jupiter.SoftAssertionsExtension
 import org.junit.jupiter.api.BeforeEach
 import org.junit.jupiter.api.Test
 import org.junit.jupiter.api.extension.ExtendWith
+import org.junit.jupiter.params.ParameterizedTest
+import org.junit.jupiter.params.provider.CsvSource
 import org.springframework.boot.test.context.SpringBootTest
 import org.springframework.boot.test.context.SpringBootTest.WebEnvironment.RANDOM_PORT
 import org.springframework.boot.test.web.server.LocalServerPort
@@ -46,7 +48,7 @@ class NodeEndpoint {
 
         // then
         result.expectStatus()
-            .isOk
+            .isCreated
             .expectBody<Node.Response>()
             .consumeWith {
                 softly.assertThat(it.responseBody?.id?.version()).isEqualTo(7)
@@ -55,4 +57,25 @@ class NodeEndpoint {
                 softly.assertThat(it.responseBody?.name).isEqualTo(name)
             }
     }
+
+    @ParameterizedTest
+    @CsvSource(
+        // not a device
+        "'00000000-0000-0000-0002-000000000000'",
+        // already a node
+        "'00000000-0000-0000-0002-000000000002'",
+    )
+    fun `added node - fail`(device: String) {
+        // given
+        val name = "Node 5"
+        val client = UUID.fromString("00000000-0000-0000-0000-000000000000")
+        val request = Node.Request(device = UUID.fromString(device), client = client, name = name)
+
+        // when
+        val result = webClient.post().uri("/node").bodyValue(request).exchange()
+
+        // then
+        result.expectStatus()
+            .isBadRequest
+    }
 }
diff --git a/src/integration-test/resources/postgres/schema.sql b/src/integration-test/resources/postgres/schema.sql
index 122ae3e..f83239a 100644
--- a/src/integration-test/resources/postgres/schema.sql
+++ b/src/integration-test/resources/postgres/schema.sql
@@ -61,4 +61,4 @@ CREATE TABLE IF NOT EXISTS public.nodes
 
 -- Index: public.i_nodes_type
 
-CREATE INDEX IF NOT EXISTS i_nodes_device ON public.nodes (device);
+CREATE UNIQUE INDEX IF NOT EXISTS i_nodes_device ON public.nodes (device);
diff --git a/src/main/kotlin/ltd/hlaeja/controller/NodeController.kt b/src/main/kotlin/ltd/hlaeja/controller/NodeController.kt
index 0f1a705..f637c61 100644
--- a/src/main/kotlin/ltd/hlaeja/controller/NodeController.kt
+++ b/src/main/kotlin/ltd/hlaeja/controller/NodeController.kt
@@ -4,8 +4,10 @@ import ltd.hlaeja.library.deviceRegistry.Node
 import ltd.hlaeja.service.NodeService
 import ltd.hlaeja.util.toEntity
 import ltd.hlaeja.util.toNodeResponse
+import org.springframework.http.HttpStatus.CREATED
 import org.springframework.web.bind.annotation.PostMapping
 import org.springframework.web.bind.annotation.RequestBody
+import org.springframework.web.bind.annotation.ResponseStatus
 import org.springframework.web.bind.annotation.RestController
 
 @RestController
@@ -14,6 +16,7 @@ class NodeController(
 ) {
 
     @PostMapping("/node")
+    @ResponseStatus(CREATED)
     suspend fun addNode(
         @RequestBody request: Node.Request,
     ): Node.Response = nodeService.addNode(request.toEntity()).toNodeResponse()
diff --git a/src/main/kotlin/ltd/hlaeja/service/NodeService.kt b/src/main/kotlin/ltd/hlaeja/service/NodeService.kt
index a8f123f..d84da2b 100644
--- a/src/main/kotlin/ltd/hlaeja/service/NodeService.kt
+++ b/src/main/kotlin/ltd/hlaeja/service/NodeService.kt
@@ -4,6 +4,8 @@ import io.github.oshai.kotlinlogging.KotlinLogging
 import java.util.UUID
 import ltd.hlaeja.entity.NodeEntity
 import ltd.hlaeja.repository.NodeRepository
+import org.springframework.dao.DataIntegrityViolationException
+import org.springframework.http.HttpStatus.BAD_REQUEST
 import org.springframework.http.HttpStatus.NOT_FOUND
 import org.springframework.stereotype.Service
 import org.springframework.web.server.ResponseStatusException
@@ -17,8 +19,11 @@ class NodeService(
 
     suspend fun addNode(
         node: NodeEntity,
-    ): NodeEntity = nodeRepository.save(node)
-        .also { log.debug { "Added node ${it.id}" } }
+    ): NodeEntity = try {
+        nodeRepository.save(node).also { log.debug { "Added node ${it.id}" } }
+    } catch (exception: DataIntegrityViolationException) {
+        throw ResponseStatusException(BAD_REQUEST, null, exception)
+    }
 
     suspend fun getNodeFromDevice(
         device: UUID,