diff --git a/mozilla/config/makefile.win b/mozilla/config/makefile.win
index e8dc2461cd4..28ea51edcc4 100644
--- a/mozilla/config/makefile.win
+++ b/mozilla/config/makefile.win
@@ -61,12 +61,12 @@ bin2rc.exe:: bin2rc.c
 
 export:: makecopy.exe mangle.exe mantomak.exe bin2rc.exe
 
-#update build number from within make script
-#    $(DEPTH)/build/build_number:: FORCE
-#        $(RM) $@
-#        $(PERL) bdate.pl > $@
-#        $(PERL) aboutime.pl $(DEPTH)/l10n/us/xp/about-all.html $@
+# update build number from within make script
+$(DEPTH)/build/build_number:: FORCE
+    $(RM) $@
+    $(PERL) bdate.pl > $@
+    $(PERL) aboutime.pl $(DEPTH)/l10n/us/xp/about-all.html $@
 
 install:: export
 
-FORCE:
+FORCE::