diff --git a/parser/html/nsHtml5TreeBuilderCppSupplement.h b/parser/html/nsHtml5TreeBuilderCppSupplement.h
index 0f90e1d1705..da81b7bc7c7 100644
--- a/parser/html/nsHtml5TreeBuilderCppSupplement.h
+++ b/parser/html/nsHtml5TreeBuilderCppSupplement.h
@@ -15,6 +15,8 @@ class nsPresContext;
 nsHtml5TreeBuilder::nsHtml5TreeBuilder(nsHtml5OplessBuilder* aBuilder)
   : scriptingEnabled(false)
   , fragment(false)
+  , contextName(nullptr)
+  , contextNamespace(kNameSpaceID_None)
   , contextNode(nullptr)
   , formPointer(nullptr)
   , headPointer(nullptr)
@@ -37,6 +39,8 @@ nsHtml5TreeBuilder::nsHtml5TreeBuilder(nsAHtml5TreeOpSink* aOpSink,
                                        nsHtml5TreeOpStage* aStage)
   : scriptingEnabled(false)
   , fragment(false)
+  , contextName(nullptr)
+  , contextNamespace(kNameSpaceID_None)
   , contextNode(nullptr)
   , formPointer(nullptr)
   , headPointer(nullptr)