diff --git a/pci/src/bus.rs b/pci/src/bus.rs
index 2ec374e6b..bc0c446fc 100644
--- a/pci/src/bus.rs
+++ b/pci/src/bus.rs
@@ -125,7 +125,7 @@ impl PciConfigIo {
             return 0xffff_ffff;
         }
 
-        let (bus, device, _function, register) =
+        let (bus, device, function, register) =
             parse_config_address(self.config_address & !0x8000_0000);
 
         // Only support one bus.
@@ -133,6 +133,11 @@ impl PciConfigIo {
             return 0xffff_ffff;
         }
 
+        // Don't support multi-function devices.
+        if function > 0 {
+            return 0xffff_ffff;
+        }
+
         self.devices.get(device).map_or(0xffff_ffff, |d| {
             d.lock().unwrap().read_config_register(register)
         })