diff --git a/cloudstack/resource_cloudstack_attach_volume.go b/cloudstack/resource_cloudstack_attach_volume.go
index 5880c912..e5916cc9 100644
--- a/cloudstack/resource_cloudstack_attach_volume.go
+++ b/cloudstack/resource_cloudstack_attach_volume.go
@@ -64,7 +64,7 @@ func resourceCloudStackAttachVolumeCreate(d *schema.ResourceData, meta interface
 
 	p := cs.Volume.NewAttachVolumeParams(d.Get("volume_id").(string), d.Get("virtual_machine_id").(string))
 	if v, ok := d.GetOk("device_id"); ok {
-		p.SetDeviceid(v.(int64))
+		p.SetDeviceid(int64(v.(int)))
 	}
 
 	r, err := cs.Volume.AttachVolume(p)
diff --git a/cloudstack/resource_cloudstack_attach_volume_unit_test.go b/cloudstack/resource_cloudstack_attach_volume_unit_test.go
new file mode 100644
index 00000000..5798d02f
--- /dev/null
+++ b/cloudstack/resource_cloudstack_attach_volume_unit_test.go
@@ -0,0 +1,46 @@
+//
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+//
+
+package cloudstack
+
+import (
+	"testing"
+
+	"github.com/apache/cloudstack-go/v2/cloudstack"
+	"github.com/hashicorp/terraform-plugin-sdk/v2/helper/schema"
+)
+
+// device_id is a schema.TypeInt, which the SDK returns as a Go int. Asserting
+// v.(int64) on it panics with "interface conversion: interface {} is int, not
+// int64" whenever a volume is attached with an explicit device_id. The create
+// function must reach the API call (and return its error) rather than panic.
+func TestAttachVolumeDeviceIdDoesNotPanic(t *testing.T) {
+	cs := cloudstack.NewClient("http://127.0.0.1:1", "key", "secret", false)
+
+	d := schema.TestResourceDataRaw(t, resourceCloudStackAttachVolume().Schema, map[string]interface{}{
+		"volume_id":          "vol-1",
+		"virtual_machine_id": "vm-1",
+		"device_id":          5,
+	})
+
+	err := resourceCloudStackAttachVolumeCreate(d, cs)
+	if err == nil {
+		t.Fatal("expected an API error from the unreachable endpoint, got nil")
+	}
+}