--- a/dom/base/nsDocument.cpp
+++ b/dom/base/nsDocument.cpp
@@ -10418,57 +10418,53 @@ static const char* kDocumentWarnings[] =
 #include "nsDocumentWarningList.h"
   nullptr
 };
 #undef DOCUMENT_WARNING
 
 bool
 nsIDocument::HasWarnedAbout(DeprecatedOperations aOperation) const
 {
-  static_assert(eDeprecatedOperationCount <= 64,
-                "Too many deprecated operations");
-  return mDeprecationWarnedAbout & (1ull << aOperation);
+  return mDeprecationWarnedAbout[aOperation];
 }
 
 void
 nsIDocument::WarnOnceAbout(DeprecatedOperations aOperation,
                            bool asError /* = false */) const
 {
   MOZ_ASSERT(NS_IsMainThread());
   if (HasWarnedAbout(aOperation)) {
     return;
   }
-  mDeprecationWarnedAbout |= (1ull << aOperation);
+  mDeprecationWarnedAbout[aOperation] = true;
   uint32_t flags = asError ? nsIScriptError::errorFlag
                            : nsIScriptError::warningFlag;
   nsContentUtils::ReportToConsole(flags,
                                   NS_LITERAL_CSTRING("DOM Core"), this,
                                   nsContentUtils::eDOM_PROPERTIES,
                                   kDeprecationWarnings[aOperation]);
 }
 
 bool
 nsIDocument::HasWarnedAbout(DocumentWarnings aWarning) const
 {
-  static_assert(eDocumentWarningCount <= 64,
-                "Too many document warnings");
-  return mDocWarningWarnedAbout & (1ull << aWarning);
+  return mDocWarningWarnedAbout[aWarning];
 }
 
 void
 nsIDocument::WarnOnceAbout(DocumentWarnings aWarning,
                            bool asError /* = false */,
                            const char16_t **aParams /* = nullptr */,
                            uint32_t aParamsLength /* = 0 */) const
 {
   MOZ_ASSERT(NS_IsMainThread());
   if (HasWarnedAbout(aWarning)) {
     return;
   }
-  mDocWarningWarnedAbout |= (1ull << aWarning);
+  mDocWarningWarnedAbout[aWarning] = true;
   uint32_t flags = asError ? nsIScriptError::errorFlag
                            : nsIScriptError::warningFlag;
   nsContentUtils::ReportToConsole(flags,
                                   NS_LITERAL_CSTRING("DOM Core"), this,
                                   nsContentUtils::eDOM_PROPERTIES,
                                   kDocumentWarnings[aWarning],
                                   aParams,
                                   aParamsLength);

--- a/dom/base/nsIDocument.h
+++ b/dom/base/nsIDocument.h
@@ -25,16 +25,17 @@
 #include "mozilla/net/ReferrerPolicy.h"  // for member
 #include "nsWeakReference.h"
 #include "mozilla/dom/DocumentBinding.h"
 #include "mozilla/WeakPtr.h"
 #include "Units.h"
 #include "nsExpirationTracker.h"
 #include "nsClassHashtable.h"
 #include "prclist.h"
+#include <bitset>                        // for member
 
 class imgIRequest;
 class nsAString;
 class nsBindingManager;
 class nsIDocShell;
 class nsDocShell;
 class nsDOMNavigationTiming;
 class nsFrameLoader;
@@ -2542,18 +2543,18 @@ public:
   }
 
   // FontFaceSource
   mozilla::dom::FontFaceSet* GetFonts(mozilla::ErrorResult& aRv);
 
   bool DidFireDOMContentLoaded() const { return mDidFireDOMContentLoaded; }
 
 private:
-  mutable uint64_t mDeprecationWarnedAbout;
-  mutable uint64_t mDocWarningWarnedAbout;
+  mutable std::bitset<eDeprecatedOperationCount> mDeprecationWarnedAbout;
+  mutable std::bitset<eDocumentWarningCount> mDocWarningWarnedAbout;
   SelectorCache mSelectorCache;
 
 protected:
   ~nsIDocument();
   nsPropertyTable* GetExtraPropertyTable(uint16_t aCategory);
 
   // Never ever call this. Only call GetWindow!
   virtual nsPIDOMWindow *GetWindowInternal() const = 0;