--- a/gfx/webrender_bindings/WebRenderTypes.h
+++ b/gfx/webrender_bindings/WebRenderTypes.h
@@ -419,40 +419,43 @@ static inline WrExternalImage NativeText
     aHandle, u0, v0, u1, v1,
     nullptr, 0
   };
 }
 
 struct VecU8 {
   WrVecU8 inner;
   VecU8() {
-    inner.data = nullptr;
-    inner.capacity = 0;
+    SetEmpty();
   }
   VecU8(VecU8&) = delete;
   VecU8(VecU8&& src) {
     inner = src.inner;
-    src.inner.data = nullptr;
-    src.inner.capacity = 0;
+    src.SetEmpty();
   }
 
   VecU8&
   operator=(VecU8&& src) {
     inner = src.inner;
-    src.inner.data = nullptr;
-    src.inner.capacity = 0;
+    src.SetEmpty();
     return *this;
   }
 
   WrVecU8
   Extract() {
     WrVecU8 ret = inner;
-    inner.data = nullptr;
+    SetEmpty();
+    return ret;
+  }
+
+  void
+  SetEmpty() {
+    inner.data = (uint8_t*)1;
     inner.capacity = 0;
-    return ret;
+    inner.length = 0;
   }
 
   ~VecU8() {
     if (inner.data) {
       wr_vec_u8_free(inner);
     }
   }
 };