tools.crossref: invalidate only with null definitions-changed

diff --git a/basis/tools/crossref/crossref.factor b/basis/tools/crossref/crossref.factor
index d6cbb9ed79369f09c31616c6c52981364e317efc..5f883aa51ce9fcdb1e9c40e2b0dbac0ab852a8b2 100644 (file)
--- a/basis/tools/crossref/crossref.factor
+++ b/basis/tools/crossref/crossref.factor
@@ -141,7 +141,7 @@ M: f smart-usage drop \ f smart-usage ;
 SINGLETON: invalidate-crossref
 
 M: invalidate-crossref definitions-changed
-    2drop f crossref set-global ;
+    drop null? [ f crossref set-global ] unless ;
 
 [ invalidate-crossref add-definition-observer ] "tools.crossref" add-startup-hook