2 files changed, 19 insertions, 5 deletions
diff --git a/dom/canvas/CanvasRenderingContext2D.cpp b/dom/canvas/CanvasRenderingContext2D.cpp
index 1a79a9f734..54711aa981 100644
--- a/dom/canvas/CanvasRenderingContext2D.cpp
+++ b/dom/canvas/CanvasRenderingContext2D.cpp
@@ -2216,14 +2216,16 @@ void CanvasRenderingContext2D::Transform(double aM11, double aM12, double aM21,
 
 already_AddRefed<DOMMatrix> CanvasRenderingContext2D::GetTransform(
     ErrorResult& aError) {
-  if (!EnsureTarget(aError)) {
+  // If we are silently failing, then we still need to return a transform while
+  // we are in the process of recovering.
+  Matrix transform;
+  if (EnsureTarget(aError)) {
+    transform = mTarget->GetTransform();
+  } else if (aError.Failed()) {
     return nullptr;
   }
 
-  MOZ_ASSERT(IsTargetValid());
-
-  RefPtr<DOMMatrix> matrix =
-      new DOMMatrix(GetParentObject(), mTarget->GetTransform());
+  RefPtr<DOMMatrix> matrix = new DOMMatrix(GetParentObject(), transform);
   return matrix.forget();
 }
 
diff --git a/dom/canvas/test/test_accelerated_canvas_context_loss.html b/dom/canvas/test/test_accelerated_canvas_context_loss.html
index 6172420bcb..610c8d8fc3 100644
--- a/dom/canvas/test/test_accelerated_canvas_context_loss.html
+++ b/dom/canvas/test/test_accelerated_canvas_context_loss.html
@@ -58,6 +58,12 @@ let countRestoredEvents = 0;
 
 function onContextLost() {
   ok(context.isContextLost(), "Canvas context should be lost during contextlost event");
+
+  try {
+    let transform = context.getTransform();
+    ok(transform.isIdentity, "Canvas context should return identity transform while context lost");
+  } catch (e) {}
+
   countLostEvents += 1;
 }
 
@@ -88,6 +94,12 @@ async function start() {
 
     ok(!context.isContextLost(), "Canvas context should not be lost after initial fill");
 
+    let transform = context.getTransform();
+    ok(transform.isIdentity, "Canvas context should default to identity transform");
+    context.setTransform(2.0, 3.0, 4.0, 5.0, 6.0, 7.0);
+    transform = context.getTransform();
+    ok(!transform.isIdentity, "Canvas context should have non-identity transform");
+
     const restarted = await restartGPUProcess();
     const expectedEvents = restarted ? 1 : 0;