diff --git a/llvm/lib/Support/YAMLTraits.cpp b/llvm/lib/Support/YAMLTraits.cpp
index 9325a09faaea0..4aaf59be2ce50 100644
--- a/llvm/lib/Support/YAMLTraits.cpp
+++ b/llvm/lib/Support/YAMLTraits.cpp
@@ -156,6 +156,8 @@ bool Input::preflightKey(const char *Key, bool Required, bool, bool &UseDefault,
   if (!CurrentNode) {
     if (Required)
       EC = make_error_code(errc::invalid_argument);
+    else
+      UseDefault = true;
     return false;
   }
 
diff --git a/llvm/unittests/Support/YAMLIOTest.cpp b/llvm/unittests/Support/YAMLIOTest.cpp
index 90c09ed7f79ee..745d743b2b244 100644
--- a/llvm/unittests/Support/YAMLIOTest.cpp
+++ b/llvm/unittests/Support/YAMLIOTest.cpp
@@ -2392,6 +2392,7 @@ TEST(YAMLIO, TestMalformedMapFailsGracefully) {
 
 struct OptionalTest {
   std::vector<int> Numbers;
+  std::optional<int> MaybeNumber;
 };
 
 struct OptionalTestSeq {
@@ -2405,6 +2406,7 @@ namespace yaml {
   struct MappingTraits<OptionalTest> {
     static void mapping(IO& IO, OptionalTest &OT) {
       IO.mapOptional("Numbers", OT.Numbers);
+      IO.mapOptional("MaybeNumber", OT.MaybeNumber);
     }
   };
 
@@ -2466,6 +2468,7 @@ TEST(YAMLIO, TestEmptyStringSucceedsForMapWithOptionalFields) {
   Input yin("");
   yin >> doc;
   EXPECT_FALSE(yin.error());
+  EXPECT_FALSE(doc.MaybeNumber.has_value());
 }
 
 TEST(YAMLIO, TestEmptyStringSucceedsForSequence) {