diff --git a/test/mozilla/mozilla.status b/test/mozilla/mozilla.status
index a119bf2a78..cfccc4603a 100644
--- a/test/mozilla/mozilla.status
+++ b/test/mozilla/mozilla.status
@@ -198,6 +198,9 @@ js1_5/Regress/regress-404755: PASS || FAIL
 js1_5/extensions/regress-363258: PASS || FAIL
 
 
+# Test that assumes specific runtime for a regexp, flaky in debug mode.
+ecma_3/RegExp/regress-85721: PASS || FAIL if $mode == debug
+
 
 ##################### INCOMPATIBLE TESTS #####################