diff --git a/mozilla/calendar/base/src/calICSService.h b/mozilla/calendar/base/src/calICSService.h
index a828bb3af06..08bcce459c1 100644
--- a/mozilla/calendar/base/src/calICSService.h
+++ b/mozilla/calendar/base/src/calICSService.h
@@ -69,7 +69,7 @@ public:
     NS_DECL_ISUPPORTS
     NS_DECL_CALIICSSERVICE
 protected:
-    mutable nsClassHashtable<nsCStringHashKey, TimezoneEntry> mTzHash;
+    nsClassHashtable<nsCStringHashKey, TimezoneEntry> mTzHash;
     TimezoneEntry const* getTimezoneEntry(nsACString const& tzid);
 };