diff --git a/babeld/util.h b/babeld/util.h
index 4e7635f..d64169b 100644
--- a/babeld/util.h
+++ b/babeld/util.h
@@ -111,6 +111,7 @@
 const char *format_address(const unsigned char *address);
 const char *format_prefix(const unsigned char *address, unsigned char prefix);
 const char *format_eui64(const unsigned char *eui);
+const char *format_bool(const int b);
 int parse_address(const char *address, unsigned char *addr_r, int *af_r);
 int parse_net(const char *ifp, unsigned char *prefix_r, unsigned char *plen_r,
               int *af_r);