diff --git a/src/build/toolset.jam b/src/build/toolset.jam
index 13073490e..5988f263f 100644
--- a/src/build/toolset.jam
+++ b/src/build/toolset.jam
@@ -189,7 +189,7 @@ rule set-target-variables ( rule-or-module target : properties * )
         # target variable even if $(result) is empty.  That is
         # undesirable because the empty target variable would mask
         # module globals intended to be used as defaults.
-        if ! $(result)-is-nonempty
+        if $(result)-is-nonempty
         {
             $(variable) on $(target) += $(result) ;
         }