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-rw-r--r--dom/base/DOMIntersectionObserver.cpp8
1 files changed, 7 insertions, 1 deletions
diff --git a/dom/base/DOMIntersectionObserver.cpp b/dom/base/DOMIntersectionObserver.cpp
index cb624fb17..0834bc05c 100644
--- a/dom/base/DOMIntersectionObserver.cpp
+++ b/dom/base/DOMIntersectionObserver.cpp
@@ -411,7 +411,13 @@ DOMIntersectionObserver::Update(nsIDocument* aDocument, DOMHighResTimeStamp time
double targetArea = targetRect.width * targetRect.height;
double intersectionArea = !intersectionRect ?
0 : intersectionRect->width * intersectionRect->height;
- double intersectionRatio = targetArea > 0.0 ? intersectionArea / targetArea : 0.0;
+
+ double intersectionRatio;
+ if (targetArea > 0.0) {
+ intersectionRatio = intersectionArea / targetArea;
+ } else {
+ intersectionRatio = intersectionRect.isSome() ? 1.0 : 0.0;
+ }
size_t threshold = -1;
if (intersectionRatio > 0.0) {