diff --git a/RELNOTES b/RELNOTES
index 7132b764..64cfb2a1 100644
--- a/RELNOTES
+++ b/RELNOTES
@@ -65,6 +65,8 @@ work on other platforms. Please report any problems and suggested fixes to
 - Failover BNDUPD messages are now discarded if they conflict with an
   update that has been trasnmitted, but not acknowledged.
 
+- A bug cleaning up unknown-xxx temporary option definitions was fixed.
+
 			Changes since 4.1.0a1
 
 - Corrected list of failover state values in dhcpd man page.
diff --git a/common/parse.c b/common/parse.c
index a781f3f7..11092ed9 100644
--- a/common/parse.c
+++ b/common/parse.c
@@ -1215,7 +1215,7 @@ parse_option_name (cfile, allocate, known, opt)
 			option = new_option(val, MDL);
 			option->universe = universe;
 			option->code = code;
-			option->format = "X";
+			option->format = default_option_format;
 			option_reference(opt, option, MDL);
 		} else
 			log_info("option %s has been redefined as option %s.  "