Index: include/llvm/Support/YAMLTraits.h
===================================================================
--- include/llvm/Support/YAMLTraits.h
+++ include/llvm/Support/YAMLTraits.h
@@ -540,12 +540,15 @@
     case '.':
     case ',':
     case ' ':
-    // TAB (0x9), LF (0xA), CR (0xD) and NEL (0x85) are allowed.
+    // TAB (0x9) is allowed.
     case 0x9:
+      continue;
+    // LF (0xA), CR (0xD) and NEL (0x85) cause parse errors when used as values
+    // in 'key: value' pairs unless double-quoted.
     case 0xA:
     case 0xD:
     case 0x85:
-      continue;
+      return QuotingType::Double;
     // DEL (0x7F) are excluded from the allowed character range.
     case 0x7F:
       return QuotingType::Double;
Index: unittests/Support/YAMLIOTest.cpp
===================================================================
--- unittests/Support/YAMLIOTest.cpp
+++ unittests/Support/YAMLIOTest.cpp
@@ -249,6 +249,54 @@
   EXPECT_TRUE(!!yin.error());
 }
 
+struct WithStringField {
+  std::string str1;
+  std::string str2;
+  std::string str3;
+  std::string str4;
+};
+
+namespace llvm {
+namespace yaml {
+template <> struct MappingTraits<WithStringField> {
+  static void mapping(IO &io, WithStringField &fb) {
+    io.mapRequired("str1", fb.str1);
+    io.mapRequired("str2", fb.str2);
+    io.mapRequired("str3", fb.str3);
+    io.mapRequired("str4", fb.str4);
+  }
+};
+} // namespace yaml
+} // namespace llvm
+
+TEST(YAMLIO, MultilineStrings) {
+  WithStringField Original;
+  Original.str1 = "a multiline string\nfoobarbaz";
+  Original.str2 = "another one\rfoobarbaz";
+  Original.str3 = "yet another one\tfoobarbaz";
+  Original.str4 = "a one-line string";
+
+  std::string Serialized;
+  {
+    llvm::raw_string_ostream OS(Serialized);
+    Output YOut(OS);
+    YOut << Original;
+  }
+
+  WithStringField Deserialized;
+  {
+    Input YIn(Serialized);
+    YIn >> Deserialized;
+    ASSERT_FALSE(YIn.error())
+        << "Parsing error occurred during deserialization. Serialized string:\n"
+        << Serialized;
+  }
+  EXPECT_EQ(Original.str1, Deserialized.str1);
+  EXPECT_EQ(Original.str2, Deserialized.str2);
+  EXPECT_EQ(Original.str3, Deserialized.str3);
+  EXPECT_EQ(Original.str4, Deserialized.str4);
+}
+
 
 //===----------------------------------------------------------------------===//
 //  Test built-in types