diff --git a/mozilla/content/html/document/src/nsHTMLDocument.cpp b/mozilla/content/html/document/src/nsHTMLDocument.cpp
index 034fcd3232b..549c3526b5f 100644
--- a/mozilla/content/html/document/src/nsHTMLDocument.cpp
+++ b/mozilla/content/html/document/src/nsHTMLDocument.cpp
@@ -292,6 +292,7 @@ nsHTMLDocument::StartDocumentLoad(nsIURL *aURL,
 #ifdef rickgdebug
     rv = NS_New_HTML_ContentSinkStream(&sink);
 #else
+    NS_PRECONDITION(nsnull != aContainer, "No content viewer container");
     aContainer->QueryInterface(kIWebShellIID, (void**)&webShell);
     rv = NS_NewHTMLContentSink(&sink, this, aURL, webShell);
     NS_IF_RELEASE(webShell);
diff --git a/mozilla/layout/html/document/src/nsHTMLDocument.cpp b/mozilla/layout/html/document/src/nsHTMLDocument.cpp
index 034fcd3232b..549c3526b5f 100644
--- a/mozilla/layout/html/document/src/nsHTMLDocument.cpp
+++ b/mozilla/layout/html/document/src/nsHTMLDocument.cpp
@@ -292,6 +292,7 @@ nsHTMLDocument::StartDocumentLoad(nsIURL *aURL,
 #ifdef rickgdebug
     rv = NS_New_HTML_ContentSinkStream(&sink);
 #else
+    NS_PRECONDITION(nsnull != aContainer, "No content viewer container");
     aContainer->QueryInterface(kIWebShellIID, (void**)&webShell);
     rv = NS_NewHTMLContentSink(&sink, this, aURL, webShell);
     NS_IF_RELEASE(webShell);