diff --git a/lib/pci.h b/lib/pci.h
index 30f5381..86d6b42 100644
--- a/lib/pci.h
+++ b/lib/pci.h
@@ -43,7 +43,7 @@
 extern void pci_bar_print(pcidevaddr_t dev, int bar_num);
 extern void pci_dev_print_id(pcidevaddr_t dev);
 
-int pci_testdev(void);
+extern int pci_testdev(void);
 
 /*
  * pci-testdev is a driver for the pci-testdev qemu pci device. The