diff --git a/testing/web-platform/meta/webvtt/parsing/cue-text-parsing/tests/tree-building.html.ini b/testing/web-platform/meta/webvtt/parsing/cue-text-parsing/tests/tree-building.html.ini
index 76f4393dff48..f380168fe107 100644
--- a/testing/web-platform/meta/webvtt/parsing/cue-text-parsing/tests/tree-building.html.ini
+++ b/testing/web-platform/meta/webvtt/parsing/cue-text-parsing/tests/tree-building.html.ini
@@ -1,6 +1,6 @@
 [tree-building.html]
   disabled:
-    if webrender and fission and os == "linux" and os_version == "18:04": https://bugzilla.mozilla.org/show_bug.cgi?id=1596532
+    if webrender and fission and os == "linux" and os_version == "18.04": https://bugzilla.mozilla.org/show_bug.cgi?id=1596532
 
   [WebVTT cue data parser test tree-building - c94512b045699cb72f730e46b2a0a3bed2c939f9]
     expected: FAIL