diff --git a/include/common/standard.h b/include/common/standard.h
index 0f4b187..cdefc9f 100644
--- a/include/common/standard.h
+++ b/include/common/standard.h
@@ -1238,6 +1238,7 @@
  *   free(err);
  */
 char *indent_msg(char **out, int level);
+int append_prefixed_str(struct buffer *out, const char *in, const char *pfx, char eol, int first);
 
 /* removes environment variable <name> from the environment as found in
  * environ. This is only provided as an alternative for systems without