diff --git a/js/src/builtin/Intl.cpp b/js/src/builtin/Intl.cpp
index be601f3592..94ef824304 100644
--- a/js/src/builtin/Intl.cpp
+++ b/js/src/builtin/Intl.cpp
@@ -3,22 +3,15 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
-/*
- * The Intl module specified by standard ECMA-402,
- * ECMAScript Internationalization API Specification.
- */
+/* Implementation of the Intl object and its non-constructor properties. */
 
 #include "builtin/Intl.h"
 
-#include "mozilla/Casting.h"
-#include "mozilla/FloatingPoint.h"
-#include "mozilla/PodOperations.h"
+#include "mozilla/Assertions.h"
+#include "mozilla/Likely.h"
 #include "mozilla/Range.h"
 
-#include <string.h>
-
 #include "jsapi.h"
-#include "jsatom.h"
 #include "jscntxt.h"
 #include "jsobj.h"
 
@@ -30,22 +23,12 @@
 #include "builtin/intl/PluralRules.h"
 #include "builtin/intl/RelativeTimeFormat.h"
 #include "builtin/intl/ScopedICUObject.h"
-#include "ds/Sort.h"
-#include "vm/DateTime.h"
 #include "vm/GlobalObject.h"
-#include "vm/Interpreter.h"
-#include "vm/Stack.h"
-#include "vm/StringBuffer.h"
-#include "vm/Unicode.h"
 
 #include "jsobjinlines.h"
 
-#include "vm/NativeObject-inl.h"
-
 using namespace js;
 
-using mozilla::IsFinite;
-
 using js::intl::CallICU;
 using js::intl::GetAvailableLocales;
 using js::intl::IcuLocale;
diff --git a/js/src/builtin/Intl.h b/js/src/builtin/Intl.h
index 938ab4de95..9ff3e74d76 100644
--- a/js/src/builtin/Intl.h
+++ b/js/src/builtin/Intl.h
@@ -6,21 +6,13 @@
 #ifndef builtin_Intl_h
 #define builtin_Intl_h
 
-#include "mozilla/HashFunctions.h"
-#include "mozilla/MemoryReporting.h"
+#include "mozilla/Attributes.h"
 
-#include "jsalloc.h"
-#include "NamespaceImports.h"
+#include "js/RootingAPI.h"
 
-#include "js/GCAPI.h"
-#include "js/GCHashTable.h"
-
-#include "unicode/utypes.h"
-
-/*
- * The Intl module specified by standard ECMA-402,
- * ECMAScript Internationalization API Specification.
- */
+struct JSContext;
+class JSObject;
+namespace JS { class Value; }
 
 namespace js {
 
@@ -29,7 +21,7 @@ namespace js {
  * Spec: ECMAScript Internationalization API Specification, 8.0, 8.1
  */
 extern JSObject*
-InitIntlClass(JSContext* cx, HandleObject obj);
+InitIntlClass(JSContext* cx, JS::Handle<JSObject*> obj);
 
 /*
  * The following functions are for use by self-hosted code.
@@ -59,7 +51,7 @@ InitIntlClass(JSContext* cx, HandleObject obj);
  * NOTE: "calendar" and "locale" properties are *not* added to the object.
  */
 extern MOZ_MUST_USE bool
-intl_GetCalendarInfo(JSContext* cx, unsigned argc, Value* vp);
+intl_GetCalendarInfo(JSContext* cx, unsigned argc, JS::Value* vp);
 
 /**
  * Returns an Array with CLDR-based fields display names.
@@ -101,34 +93,7 @@ intl_GetCalendarInfo(JSContext* cx, unsigned argc, Value* vp);
  * ]
  */
 extern MOZ_MUST_USE bool
-intl_ComputeDisplayNames(JSContext* cx, unsigned argc, Value* vp);
-
-/**
- * Cast char16_t* strings to UChar* strings used by ICU.
- */
-inline const UChar*
-Char16ToUChar(const char16_t* chars)
-{
-  return reinterpret_cast<const UChar*>(chars);
-}
-
-inline UChar*
-Char16ToUChar(char16_t* chars)
-{
-  return reinterpret_cast<UChar*>(chars);
-}
-
-inline char16_t*
-UCharToChar16(UChar* chars)
-{
-  return reinterpret_cast<char16_t*>(chars);
-}
-
-inline const char16_t*
-UCharToChar16(const UChar* chars)
-{
-  return reinterpret_cast<const char16_t*>(chars);
-}
+intl_ComputeDisplayNames(JSContext* cx, unsigned argc, JS::Value* vp);
 
 } // namespace js
 
diff --git a/js/src/builtin/intl/ICUHeader.h b/js/src/builtin/intl/ICUHeader.h
index 0a0e280838..08fe2c1719 100644
--- a/js/src/builtin/intl/ICUHeader.h
+++ b/js/src/builtin/intl/ICUHeader.h
@@ -20,4 +20,31 @@
 #include "unicode/ureldatefmt.h"
 #include "unicode/ustring.h"
 
+/**
+ * Cast char16_t* strings to UChar* strings used by ICU.
+ */
+inline const UChar*
+Char16ToUChar(const char16_t* chars)
+{
+  return reinterpret_cast<const UChar*>(chars);
+}
+
+inline UChar*
+Char16ToUChar(char16_t* chars)
+{
+  return reinterpret_cast<UChar*>(chars);
+}
+
+inline char16_t*
+UCharToChar16(UChar* chars)
+{
+  return reinterpret_cast<char16_t*>(chars);
+}
+
+inline const char16_t*
+UCharToChar16(const UChar* chars)
+{
+  return reinterpret_cast<const char16_t*>(chars);
+}
+
 #endif /* builtin_intl_ICUHeader_h */
diff --git a/js/src/jsstr.cpp b/js/src/jsstr.cpp
index b9e10b61b9..6726da9457 100644
--- a/js/src/jsstr.cpp
+++ b/js/src/jsstr.cpp
@@ -30,7 +30,7 @@
 #include "jstypes.h"
 #include "jsutil.h"
 
-#include "builtin/Intl.h"
+#include "builtin/intl/ICUHeader.h"
 #include "builtin/RegExp.h"
 #include "jit/InlinableNatives.h"
 #include "js/Conversions.h"