diff --git a/dom/bindings/Codegen.py b/dom/bindings/Codegen.py
index 72297cb735ee..832be912d07b 100644
--- a/dom/bindings/Codegen.py
+++ b/dom/bindings/Codegen.py
@@ -14059,7 +14059,7 @@ def initIdsClassMethod(identifiers, atomCacheName):
     idinit.reverse()
     body = fill(
         """
-        MOZ_ASSERT(!*reinterpret_cast<jsid**>(atomsCache));
+        MOZ_ASSERT(JSID_IS_VOID(*reinterpret_cast<jsid*>(atomsCache)));
 
         // Initialize these in reverse order so that any failure leaves the first one
         // uninitialized.
@@ -14149,7 +14149,8 @@ class CGDictionary(CGThing):
                 ${dictName}Atoms* atomsCache = nullptr;
                 if (cx) {
                   atomsCache = GetAtomCache<${dictName}Atoms>(cx);
-                  if (!*reinterpret_cast<jsid**>(atomsCache) && !InitIds(cx, atomsCache)) {
+                  if (JSID_IS_VOID(*reinterpret_cast<jsid*>(atomsCache)) &&
+                      !InitIds(cx, atomsCache)) {
                     return false;
                   }
                 }
@@ -14332,7 +14333,8 @@ class CGDictionary(CGThing):
             body += fill(
                 """
                 ${dictName}Atoms* atomsCache = GetAtomCache<${dictName}Atoms>(cx);
-                if (!*reinterpret_cast<jsid**>(atomsCache) && !InitIds(cx, atomsCache)) {
+                if (JSID_IS_VOID(*reinterpret_cast<jsid*>(atomsCache)) &&
+                    !InitIds(cx, atomsCache)) {
                   return false;
                 }
 
@@ -17712,7 +17714,8 @@ class CallbackOperationBase(CallbackMethod):
         getCallableFromProp = fill(
             """
             ${atomCacheName}* atomsCache = GetAtomCache<${atomCacheName}>(cx);
-            if ((!*reinterpret_cast<jsid**>(atomsCache) && !InitIds(cx, atomsCache)) ||
+            if ((JSID_IS_VOID(*reinterpret_cast<jsid*>(atomsCache)) &&
+                 !InitIds(cx, atomsCache)) ||
                 !GetCallableProperty(cx, atomsCache->${methodAtomName}, &callable)) {
               aRv.Throw(NS_ERROR_UNEXPECTED);
               return${errorReturn};
@@ -17794,7 +17797,8 @@ class CallbackGetter(CallbackAccessor):
             """
             JS::Rooted<JSObject *> callback(cx, mCallback);
             ${atomCacheName}* atomsCache = GetAtomCache<${atomCacheName}>(cx);
-            if ((!*reinterpret_cast<jsid**>(atomsCache) && !InitIds(cx, atomsCache)) ||
+            if ((JSID_IS_VOID(*reinterpret_cast<jsid*>(atomsCache))
+                 && !InitIds(cx, atomsCache)) ||
                 !JS_GetPropertyById(cx, callback, atomsCache->${attrAtomName}, &rval)) {
               aRv.Throw(NS_ERROR_UNEXPECTED);
               return${errorReturn};
@@ -17822,7 +17826,8 @@ class CallbackSetter(CallbackAccessor):
             """
             MOZ_ASSERT(argv.length() == 1);
             ${atomCacheName}* atomsCache = GetAtomCache<${atomCacheName}>(cx);
-            if ((!*reinterpret_cast<jsid**>(atomsCache) && !InitIds(cx, atomsCache)) ||
+            if ((JSID_IS_VOID(*reinterpret_cast<jsid*>(atomsCache)) &&
+                 !InitIds(cx, atomsCache)) ||
                 !JS_SetPropertyById(cx, CallbackKnownNotGray(), atomsCache->${attrAtomName}, argv[0])) {
               aRv.Throw(NS_ERROR_UNEXPECTED);
               return${errorReturn};
diff --git a/xpcom/base/CycleCollectedJSContext.cpp b/xpcom/base/CycleCollectedJSContext.cpp
index 41aa87230258..9661aefa8755 100644
--- a/xpcom/base/CycleCollectedJSContext.cpp
+++ b/xpcom/base/CycleCollectedJSContext.cpp
@@ -62,10 +62,6 @@ CycleCollectedJSContext::CycleCollectedJSContext()
       mMicroTaskRecursionDepth(0) {
   MOZ_COUNT_CTOR(CycleCollectedJSContext);
 
-  // Reinitialize PerThreadAtomCache because dom/bindings/Codegen.py compares
-  // against zero rather than JSID_VOID to detect uninitialized jsid members.
-  memset(static_cast<PerThreadAtomCache*>(this), 0, sizeof(PerThreadAtomCache));
-
   nsCOMPtr<nsIThread> thread = do_GetCurrentThread();
   mOwningThread = thread.forget().downcast<nsThread>().take();
   MOZ_RELEASE_ASSERT(mOwningThread);