diff --git a/layout/base/nsDocumentViewer.cpp b/layout/base/nsDocumentViewer.cpp
index a1105ae524..782ac332ce 100644
--- a/layout/base/nsDocumentViewer.cpp
+++ b/layout/base/nsDocumentViewer.cpp
@@ -544,6 +544,12 @@ nsDocumentViewer::~nsDocumentViewer()
     mDocument->Destroy();
   }
 
+  if (mPrintEngine) {
+    mPrintEngine->Destroy();
+    mPrintEngine = nullptr;
+  }
+
+  MOZ_RELEASE_ASSERT(mDestroyRefCount == 0);
   NS_ASSERTION(!mPresShell && !mPresContext,
                "User did not call nsIContentViewer::Destroy");
   if (mPresShell || mPresContext) {