diff --git a/llvm/lib/Support/YAMLTraits.cpp b/llvm/lib/Support/YAMLTraits.cpp
--- a/llvm/lib/Support/YAMLTraits.cpp
+++ b/llvm/lib/Support/YAMLTraits.cpp
@@ -166,6 +166,8 @@
   if (!MN) {
     if (Required || !isa<EmptyHNode>(CurrentNode))
       setError(CurrentNode, "not a mapping");
+    else
+      UseDefault = true;
     return false;
   }
   MN->ValidKeys.push_back(Key);
diff --git a/llvm/test/ObjectYAML/MachO/DWARF-pubsections.yaml b/llvm/test/ObjectYAML/MachO/DWARF-pubsections.yaml
--- a/llvm/test/ObjectYAML/MachO/DWARF-pubsections.yaml
+++ b/llvm/test/ObjectYAML/MachO/DWARF-pubsections.yaml
@@ -356,7 +356,8 @@
 ## contents, if the "debug_pubnames"/"debug_pubtypes" entry doesn't exist in the
 ## "DWARF" entry.
 
-# RUN: yaml2obj --docnum=2 %s | obj2yaml | FileCheck %s --check-prefix=EMPTY
+# RUN: yaml2obj --docnum=2 %s -o %t2
+# RUN: obj2yaml %t2 | FileCheck %s --check-prefix=EMPTY
 
 #      EMPTY: Sections:
 # EMPTY-NEXT:   - sectname:        __debug_pubnames
@@ -394,7 +395,7 @@
   cpusubtype: 0x00000003
   filetype:   0x0000000A
   ncmds:      1
-  sizeofcmds: 1800
+  sizeofcmds: 1772
   flags:      0x00000000
   reserved:   0x00000000
 LoadCommands: