--- a/mail/app/Makefile.in
+++ b/mail/app/Makefile.in
@@ -396,12 +396,12 @@ endif
 libs:: $(srcdir)/profile/prefs.js
 	$(INSTALL) $^ $(DIST)/bin/defaults/profile
 
 install:: $(srcdir)/profile/prefs.js
 	$(SYSINSTALL) $(IFLAGS1) $^  $(DESTDIR)$(mozappdir)/defaults/profile
 
 # Disable these tests due to bug 431125
 libs::
-	echo "function run_test() {dump('disabled for bug 431125');}" >$(DIST)/../_tests/xpcshell-simple/test_cookies/unit/test_cookies.js
-	echo "function run_test() {dump('disabled for TB for bug 431125');}" >$(DIST)/../_tests/xpcshell-simple/test_necko/unit/test_cookie_header.js
+	if test -f $(DIST)/../_tests/xpcshell-simple/test_cookies/unit/test_cookies.js; then echo "function run_test() {dump('disabled for bug 431125');}" >$(DIST)/../_tests/xpcshell-simple/test_cookies/unit/test_cookies.js; fi;
+	if test -f $(DIST)/../_tests/xpcshell-simple/test_necko/unit/test_cookie_header.js; then echo "function run_test() {dump('disabled for TB for bug 431125');}" >$(DIST)/../_tests/xpcshell-simple/test_necko/unit/test_cookie_header.js; fi;
 	$(RM) $(DIST)/bin/TestCookie
 	cp $(DIST)/bin/TestTArray $(DIST)/bin/TestCookie