diff --git a/src/build/feature.jam b/src/build/feature.jam
index f2960a5ef..4982524a4 100644
--- a/src/build/feature.jam
+++ b/src/build/feature.jam
@@ -161,6 +161,20 @@ rule feature (
 rule set-default ( feature : value )
 {
     local f = [ grist $(feature) ] ;
+    local a = $($(f).attributes) ;
+    local bad-attribute = ;
+    if free in $(a)
+    {
+        bad-attribute = free ;
+    }
+    else if optional in $(a)
+    {
+        bad-attribute = optional ;
+    }
+    if $(bad-attribute)
+    {
+        errors.error "$(bad-attribute) property $(f) cannot have a default." ;
+    }
     if ! $(value) in $($(f).values)
     {
         errors.error "The specified default value, '$(value)' is invalid"