diff --git a/include/common/standard.h b/include/common/standard.h
index 69d760dd8..da2efcfbb 100644
--- a/include/common/standard.h
+++ b/include/common/standard.h
@@ -372,6 +372,16 @@ extern const char *invalid_domainchar(const char *name);
  */
 extern const char *invalid_prefix_char(const char *name);
 
+/* returns true if <c> is an identifier character, that is, a digit, a letter,
+ * or '-', '_', ':' or '.'. This is usable for proxy names, server names, ACL
+ * names, sample fetch names, and converter names.
+ */
+static inline int is_idchar(char c)
+{
+	return isalnum((int)(unsigned char)c) ||
+	       c == '.' || c == '_' || c == '-' || c == ':';
+}
+
 /*
  * converts <str> to a locally allocated struct sockaddr_storage *, and a
  * port range consisting in two integers. The low and high end are always set