diff --git a/docs/environment.md b/docs/environment.md
index a9cac929..35b91a8d 100644
--- a/docs/environment.md
+++ b/docs/environment.md
@@ -112,6 +112,7 @@ An empty default means the variable is unset and its value is determined automat
 | Variable | Default | Description |
 |---|---|---|
 | `MACHINE` | `q35` | QEMU machine type. |
+| `PCI_BUS` | `pcie.0` | Overrides the PCI bus used for attached devices. |
 | `UUID` |  | UUID assigned to Windows. |
 | `HPET` | `off` | QEMU HPET timer setting. |
 | `VMPORT` | `off` | QEMU VMware port setting. |