diff --git a/src/htsmsg.c b/src/htsmsg.c
index 1976dda0..c74a3afc 100644
--- a/src/htsmsg.c
+++ b/src/htsmsg.c
@@ -393,6 +393,7 @@ htsmsg_field_get_string(htsmsg_field_t *f)
     snprintf(buf, sizeof(buf), "%"PRId64, f->hmf_s64);
     f->hmf_str = strdup(buf);
     f->hmf_type = HMF_STR;
+    f->hmf_flags |= HMF_ALLOCED;
     break;
   }
   return f->hmf_str;