diff --git a/lib/prefix.h b/lib/prefix.h
index bc8aebc..a517d79 100644
--- a/lib/prefix.h
+++ b/lib/prefix.h
@@ -170,6 +170,7 @@
 #endif /*s6_addr32*/
 
 /* Prototypes. */
+extern int str2family(const char *);
 extern int afi2family (afi_t);
 extern afi_t family2afi (int);