new file mode 100644
--- /dev/null
+++ b/layout/reftests/svg/mask-contains-inner-svg-01.svg
@@ -0,0 +1,13 @@
+<?xml version="1.0"?>
+<svg xmlns="http://www.w3.org/2000/svg">
+  <defs>
+    <mask id="myMask">
+      <svg x="50%" overflow="visible">
+        <polygon fill="white" points="-50 0 50 0 50 100 -50 100"/>
+      </svg>
+    </mask>
+  </defs>
+  <rect width="100%" height="100%" fill="lime"/>
+  <circle cx="50%" cy="50" r="40" fill="red"/>
+  <rect mask="url(#myMask)" width="100%" height="100%" fill="lime"/>
+</svg>

new file mode 100644
--- /dev/null
+++ b/layout/reftests/svg/mask-contains-inner-svg-02.svg
@@ -0,0 +1,15 @@
+<?xml version="1.0"?>
+<svg xmlns="http://www.w3.org/2000/svg">
+  <defs>
+    <mask id="myMask">
+      <svg x="25%" overflow="visible">
+        <svg x="25%" overflow="visible">
+          <polygon fill="white" points="-50 0 50 0 50 100 -50 100"/>
+        </svg>
+      </svg>
+    </mask>
+  </defs>
+  <rect width="100%" height="100%" fill="lime"/>
+  <circle cx="50%" cy="50" r="40" fill="red"/>
+  <rect mask="url(#myMask)" width="100%" height="100%" fill="lime"/>
+</svg>

--- a/layout/reftests/svg/reftest.list
+++ b/layout/reftests/svg/reftest.list
@@ -462,8 +462,10 @@ default-preferences
 != nested-mask-mode.svg about:blank
 == mask-empty-size.svg about:blank
 
 == paint-on-maskLayer-1a.html paint-on-maskLayer-1-ref.html
 == paint-on-maskLayer-1b.html paint-on-maskLayer-1-ref.html
 == paint-on-maskLayer-1c.html paint-on-maskLayer-1-ref.html
 
 fuzzy(71,817) == filter-on-continuation-box-01.html filter-on-continuation-box-ref.html
+== mask-contains-inner-svg-01.svg pass.svg
+== mask-contains-inner-svg-02.svg pass.svg