diff --git a/gfx/thebes/gfxFcPlatformFontList.cpp b/gfx/thebes/gfxFcPlatformFontList.cpp
index f1b461a4c15f..182712a910d3 100644
--- a/gfx/thebes/gfxFcPlatformFontList.cpp
+++ b/gfx/thebes/gfxFcPlatformFontList.cpp
@@ -2423,23 +2423,8 @@ gfxFcPlatformFontList::TryLangForGroup(const nsACString& aOSLang,
         ++pos;
     }
 
-    // We can safely use mLangService->LookupLanguage if we're on the main
-    // thread, or if we're in a Servo traversal that has locked the cache,
-    // but not if we're on the font enumeration thread used to populate the
-    // Font menu in about:preferences.
-    if (IsInServoTraversalWithoutMainThreadAssertion() || NS_IsMainThread()) {
-        nsAtom *atom = mLangService->LookupLanguage(aFcLang);
-        return atom == aLangGroup;
-    }
-
-    // Off-main-thread/non-servo-traversal version: fall back to
-    // GetUncachedLanguageGroup to avoid unsafe access to the lang-group
-    // mapping cache hashtable.
-    nsAutoCString lowered(aFcLang);
-    ToLowerCase(lowered);
-    RefPtr<nsAtom> lang = NS_Atomize(lowered);
-    RefPtr<nsAtom> group = mLangService->GetUncachedLanguageGroup(lang);
-    return group.get() == aLangGroup;
+    nsAtom *atom = mLangService->LookupLanguage(aFcLang);
+    return atom == aLangGroup;
 }
 
 void
diff --git a/layout/style/ServoUtils.h b/layout/style/ServoUtils.h
index fa10f2fe2d8c..71c665c12cac 100644
--- a/layout/style/ServoUtils.h
+++ b/layout/style/ServoUtils.h
@@ -33,14 +33,6 @@ inline bool IsInServoTraversal()
   MOZ_ASSERT(sInServoTraversal || NS_IsMainThread());
   return sInServoTraversal;
 }
-
-inline bool IsInServoTraversalWithoutMainThreadAssertion()
-{
-  // This is for cases when we _only_ want to query whether we're in Servo
-  // traversal, without asserting in the case of other non-main-thread callers.
-  // Use this only if the calling code is safe to use off the main thread.
-  return sInServoTraversal;
-}
 } // namespace mozilla
 
 #define MOZ_DECL_STYLO_CONVERT_METHODS_SERVO(servotype_) \