diff --git a/src/option.c b/src/option.c
index ac2ba20..9e315a5 100644
--- a/src/option.c
+++ b/src/option.c
@@ -663,7 +663,7 @@ static char *canonicalise_opt(char *s)
     return 0;
 
   if (strlen(s) == 0)
-    return opt_string_alloc("");
+    return opt_malloc(1); /* Heap-allocated empty string */
 
   unhide_metas(s);
   if (!(ret = canonicalise(s, &nomem)) && nomem)