diff --git a/builder/proxmox/common/config.go b/builder/proxmox/common/config.go
index c4978595..f35c3bcf 100644
--- a/builder/proxmox/common/config.go
+++ b/builder/proxmox/common/config.go
@@ -512,6 +512,7 @@ func (c *Config) Prepare(upper interface{}, raws ...interface{}) ([]string, []st
 		}
 	}
 
+	// See https://pve.proxmox.com/pve-docs/api-viewer/index.html#/nodes/{node}/hardware/pci/{pciid}
 	validPCIIDre := regexp.MustCompile(`^(?:[0-9a-fA-F]{4}:)?[0-9a-fA-F]{2}:[0-9a-fA-F]{2}\.[0-9a-fA-F]$`)
 	for _, device := range c.PCIDevices {
 		if device.Host == "" && device.Mapping == "" {