Index: lib/ObjectYAML/ObjectYAML.cpp
===================================================================
--- lib/ObjectYAML/ObjectYAML.cpp
+++ lib/ObjectYAML/ObjectYAML.cpp
@@ -51,7 +51,9 @@
       MappingTraits<WasmYAML::Object>::mapping(IO, *ObjectFile.Wasm);
     } else {
       Input &In = (Input &)IO;
-      std::string Tag = In.getCurrentNode()->getRawTag();
+      std::string Tag;
+      if (In.getCurrentNode())
+        Tag = In.getCurrentNode()->getRawTag();
       if (Tag.empty())
         IO.setError("YAML Object File missing document type tag!");
       else
Index: lib/Support/YAMLParser.cpp
===================================================================
--- lib/Support/YAMLParser.cpp
+++ lib/Support/YAMLParser.cpp
@@ -1769,10 +1769,8 @@
 bool Stream::failed() { return scanner->failed(); }
 
 void Stream::printError(Node *N, const Twine &Msg) {
-  scanner->printError( N->getSourceRange().Start
-                     , SourceMgr::DK_Error
-                     , Msg
-                     , N->getSourceRange());
+  scanner->printError(N ? N->getSourceRange().Start : SMLoc(),
+                      SourceMgr::DK_Error, Msg, N ? N->getSourceRange() : None);
 }
 
 document_iterator Stream::begin() {
Index: lib/Support/YAMLTraits.cpp
===================================================================
--- lib/Support/YAMLTraits.cpp
+++ lib/Support/YAMLTraits.cpp
@@ -113,6 +113,8 @@
 }
 
 bool Input::mapTag(StringRef Tag, bool Default) {
+  if (!CurrentNode)
+    return false;
   std::string foundTag = CurrentNode->_node->getVerbatimTag();
   if (foundTag.empty()) {
     // If no tag found and 'Tag' is the default, say it was found.
@@ -340,8 +342,7 @@
 void Input::blockScalarString(StringRef &S) { scalarString(S, false); }
 
 void Input::setError(HNode *hnode, const Twine &message) {
-  assert(hnode && "HNode must not be NULL");
-  this->setError(hnode->_node, message);
+  this->setError(hnode ? hnode->_node : (Node *)nullptr, message);
 }
 
 void Input::setError(Node *node, const Twine &message) {
Index: test/Object/yaml2obj-invalid2.yaml
===================================================================
--- test/Object/yaml2obj-invalid2.yaml
+++ test/Object/yaml2obj-invalid2.yaml
@@ -0,0 +1,2 @@
+# RUN: not yaml2obj %s 2>&1 | FileCheck %s
+# CHECK: <unknown>:0: error: YAML Object File missing document type tag!