diff --git a/lib/prefix.h b/lib/prefix.h
index a7598b7..5f1ff05 100644
--- a/lib/prefix.h
+++ b/lib/prefix.h
@@ -144,8 +144,8 @@
 }
 
 /* Prototypes. */
-extern int afi2family (int);
-extern int family2afi (int);
+extern int afi2family (afi_t);
+extern afi_t family2afi (int);
 
 extern struct prefix *prefix_new (void);
 extern void prefix_free (struct prefix *);