diff --git a/lib/utils.c b/lib/utils.c
index 73ce865..df8795a 100644
--- a/lib/utils.c
+++ b/lib/utils.c
@@ -241,6 +241,7 @@
 				err = -1;
 				goto done;
 			}
+			dst->flags |= PREFIXLEN_SPECIFIED;
 			dst->bitlen = plen;
 		}
 	}