diff --git a/mfbt/Range.h b/mfbt/Range.h
index 149870f4d435..ba6028fa2389 100644
--- a/mfbt/Range.h
+++ b/mfbt/Range.h
@@ -26,6 +26,14 @@ public:
     : mStart(aPtr, aPtr, aPtr + aLength),
       mEnd(aPtr + aLength, aPtr, aPtr + aLength)
   {}
+  Range(const RangedPtr<T>& aStart, const RangedPtr<T>& aEnd)
+    : mStart(aStart.get(), aStart.get(), aEnd.get()),
+      mEnd(aEnd.get(), aStart.get(), aEnd.get())
+  {
+    // Only accept two RangedPtrs within the same range.
+    aStart.checkIdenticalRange(aEnd);
+    MOZ_ASSERT(aStart <= aEnd);
+  }
 
   RangedPtr<T> start() const { return mStart; }
   RangedPtr<T> end() const { return mEnd; }
diff --git a/mfbt/RangedPtr.h b/mfbt/RangedPtr.h
index 4ac3c9e35b61..a07c1f4f85a2 100644
--- a/mfbt/RangedPtr.h
+++ b/mfbt/RangedPtr.h
@@ -117,6 +117,12 @@ public:
 
   explicit operator bool() const { return mPtr != nullptr; }
 
+  void checkIdenticalRange(const RangedPtr<T>& aOther) const
+  {
+    MOZ_ASSERT(mRangeStart == aOther.mRangeStart);
+    MOZ_ASSERT(mRangeEnd == aOther.mRangeEnd);
+  }
+
   /*
    * You can only assign one RangedPtr into another if the two pointers have
    * the same valid range:
@@ -129,8 +135,7 @@ public:
    */
   RangedPtr<T>& operator=(const RangedPtr<T>& aOther)
   {
-    MOZ_ASSERT(mRangeStart == aOther.mRangeStart);
-    MOZ_ASSERT(mRangeEnd == aOther.mRangeEnd);
+    checkIdenticalRange(aOther);
     mPtr = aOther.mPtr;
     checkSanity();
     return *this;