Index: include/llvm/Support/YAMLTraits.h
===================================================================
--- include/llvm/Support/YAMLTraits.h
+++ include/llvm/Support/YAMLTraits.h
@@ -1418,8 +1418,8 @@
                                Input &>::type
 operator>>(Input &yin, T &docMap) {
   EmptyContext Ctx;
-  yin.setCurrentDocument();
-  yamlize(yin, docMap, true, Ctx);
+  if (yin.setCurrentDocument())
+    yamlize(yin, docMap, true, Ctx);
   return yin;
 }
 
Index: test/Object/yaml2obj-invalid.yaml
===================================================================
--- test/Object/yaml2obj-invalid.yaml
+++ test/Object/yaml2obj-invalid.yaml
@@ -0,0 +1,2 @@
+# RUN: not yaml2obj %s 2>&1 | FileCheck %s
+# CHECK: Unknown document type!