diff --git a/util/string-util.c b/util/string-util.c
index 3e7066cd..a90501ee 100644
--- a/util/string-util.c
+++ b/util/string-util.c
@@ -37,6 +37,14 @@ strtok_len (char *s, const char *delim, size_t *len)
     return *len ? s : NULL;
 }
 
+const char *
+strtok_len_c (const char *s, const char *delim, size_t *len)
+{
+    /* strtok_len is already const-safe, but we can't express both
+     * versions in the C type system. */
+    return strtok_len ((char*)s, delim, len);
+}
+
 char *
 sanitize_string (const void *ctx, const char *str)
 {
diff --git a/util/string-util.h b/util/string-util.h
index ccad17f1..e409cb3d 100644
--- a/util/string-util.h
+++ b/util/string-util.h
@@ -23,6 +23,9 @@ extern "C" {
 
 char *strtok_len (char *s, const char *delim, size_t *len);
 
+/* Const version of strtok_len. */
+const char *strtok_len_c (const char *s, const char *delim, size_t *len);
+
 /* Return a talloced string with str sanitized.
  *
  * Whitespace characters (tabs and newlines) are replaced with spaces,