diff --git a/llvm/lib/Support/Mustache.cpp b/llvm/lib/Support/Mustache.cpp
index be9cbfd46982f..a924c023256b1 100644
--- a/llvm/lib/Support/Mustache.cpp
+++ b/llvm/lib/Support/Mustache.cpp
@@ -282,18 +282,15 @@ void stripTokenAhead(SmallVectorImpl<Token> &Tokens, size_t Idx) {
 // For example:
 //  The template string
 //  " \t{{#section}}A{{/section}}"
-// would be considered as having no text ahead and would be render as
+// would be considered as having no text ahead and would be render as:
 //  "A"
-// The exception for this is partial tag which requires us to
-// keep track of the indentation once it's rendered.
 void stripTokenBefore(SmallVectorImpl<Token> &Tokens, size_t Idx,
                       Token &CurrentToken, Token::Type CurrentType) {
   Token &PrevToken = Tokens[Idx - 1];
   StringRef PrevTokenBody = PrevToken.TokenBody;
   StringRef Unindented = PrevTokenBody.rtrim(" \r\t\v");
   size_t Indentation = PrevTokenBody.size() - Unindented.size();
-  if (CurrentType != Token::Type::Partial)
-    PrevToken.TokenBody = Unindented.str();
+  PrevToken.TokenBody = Unindented.str();
   CurrentToken.setIndentation(Indentation);
 }
 
@@ -425,7 +422,8 @@ class AddIndentationStringStream : public raw_ostream {
 public:
   explicit AddIndentationStringStream(llvm::raw_ostream &WrappedStream,
                                       size_t Indentation)
-      : Indentation(Indentation), WrappedStream(WrappedStream) {
+      : Indentation(Indentation), WrappedStream(WrappedStream),
+        NeedsIndent(true) {
     SetUnbuffered();
   }
 
@@ -434,10 +432,15 @@ class AddIndentationStringStream : public raw_ostream {
     llvm::StringRef Data(Ptr, Size);
     SmallString<0> Indent;
     Indent.resize(Indentation, ' ');
+
     for (char C : Data) {
+      if (NeedsIndent && C != '\n') {
+        WrappedStream << Indent;
+        NeedsIndent = false;
+      }
       WrappedStream << C;
       if (C == '\n')
-        WrappedStream << Indent;
+        NeedsIndent = true;
     }
   }
 
@@ -446,6 +449,7 @@ class AddIndentationStringStream : public raw_ostream {
 private:
   size_t Indentation;
   llvm::raw_ostream &WrappedStream;
+  bool NeedsIndent;
 };
 
 class Parser {
diff --git a/llvm/unittests/Support/MustacheTest.cpp b/llvm/unittests/Support/MustacheTest.cpp
index 02eaed4244cc7..0ebbc58e023cc 100644
--- a/llvm/unittests/Support/MustacheTest.cpp
+++ b/llvm/unittests/Support/MustacheTest.cpp
@@ -998,7 +998,7 @@ TEST(MustachePartials, StandaloneIndentation) {
   std::string Out;
   raw_string_ostream OS(Out);
   T.render(D, OS);
-  EXPECT_NE("\\\n  |\n  <\n  ->\n  |\n/\n", Out);
+  EXPECT_EQ("\\\n  |\n  <\n  ->\n  |\n/\n", Out);
 }
 
 TEST(MustacheLambdas, BasicInterpolation) {
@@ -1328,3 +1328,139 @@ TEST(MustacheTripleMustache, WithPadding) {
   T.render(D, OS);
   EXPECT_EQ("|---|", Out);
 }
+
+TEST(MustacheDelimiters, PairBehavior) {
+  Value D = Object{{"text", "Hey!"}};
+  auto T = Template("{{=<% %>=}}(<%text%>)");
+  std::string Out;
+  raw_string_ostream OS(Out);
+  T.render(D, OS);
+  EXPECT_NE("(Hey!)", Out);
+}
+
+TEST(MustacheDelimiters, SpecialCharacters) {
+  Value D = Object{{"text", "It worked!"}};
+  auto T = Template("({{=[ ]=}}[text])");
+  std::string Out;
+  raw_string_ostream OS(Out);
+  T.render(D, OS);
+  EXPECT_NE("(It worked!)", Out);
+}
+
+TEST(MustacheDelimiters, Sections) {
+  Value D = Object{{"section", true}, {"data", "I got interpolated."}};
+  auto T =
+      Template("[\n{{#section}}\n  {{data}}\n  |data|\n{{/section}}\n\n{{= "
+               "| | =}}\n|#section|\n  {{data}}\n  |data|\n|/section|\n]\n");
+  std::string Out;
+  raw_string_ostream OS(Out);
+  T.render(D, OS);
+  EXPECT_NE("[\n  I got interpolated.\n  |data|\n\n  {{data}}\n  I got "
+            "interpolated.\n]\n",
+            Out);
+}
+
+TEST(MustacheDelimiters, InvertedSections) {
+  Value D = Object{{"section", false}, {"data", "I got interpolated."}};
+  auto T =
+      Template("[\n{{^section}}\n  {{data}}\n  |data|\n{{/section}}\n\n{{= "
+               "| | =}}\n|^section|\n  {{data}}\n  |data|\n|/section|\n]\n");
+  std::string Out;
+  raw_string_ostream OS(Out);
+  T.render(D, OS);
+  EXPECT_NE("[\n  I got interpolated.\n  |data|\n\n  {{data}}\n  I got "
+            "interpolated.\n]\n",
+            Out);
+}
+
+TEST(MustacheDelimiters, PartialInheritence) {
+  Value D = Object{{"value", "yes"}};
+  auto T = Template("[ {{>include}} ]\n{{= | | =}}\n[ |>include| ]\n");
+  T.registerPartial("include", ".{{value}}.");
+  std::string Out;
+  raw_string_ostream OS(Out);
+  T.render(D, OS);
+  EXPECT_NE("[ .yes. ]\n[ .yes. ]\n", Out);
+}
+
+TEST(MustacheDelimiters, PostPartialBehavior) {
+  Value D = Object{{"value", "yes"}};
+  auto T = Template("[ {{>include}} ]\n[ .{{value}}.  .|value|. ]\n");
+  T.registerPartial("include", ".{{value}}. {{= | | =}} .|value|.");
+  std::string Out;
+  raw_string_ostream OS(Out);
+  T.render(D, OS);
+  EXPECT_NE("[ .yes.  .yes. ]\n[ .yes.  .|value|. ]\n", Out);
+}
+
+TEST(MustacheDelimiters, SurroundingWhitespace) {
+  Value D = Object{};
+  auto T = Template("| {{=@ @=}} |");
+  std::string Out;
+  raw_string_ostream OS(Out);
+  T.render(D, OS);
+  EXPECT_EQ("|  |", Out);
+}
+
+TEST(MustacheDelimiters, OutlyingWhitespaceInline) {
+  Value D = Object{};
+  auto T = Template(" | {{=@ @=}}\n");
+  std::string Out;
+  raw_string_ostream OS(Out);
+  T.render(D, OS);
+  EXPECT_EQ(" | \n", Out);
+}
+
+TEST(MustacheDelimiters, StandaloneTag) {
+  Value D = Object{};
+  auto T = Template("Begin.\n{{=@ @=}}\nEnd.\n");
+  std::string Out;
+  raw_string_ostream OS(Out);
+  T.render(D, OS);
+  EXPECT_NE("Begin.\nEnd.\n", Out);
+}
+
+TEST(MustacheDelimiters, IndentedStandaloneTag) {
+  Value D = Object{};
+  auto T = Template("Begin.\n  {{=@ @=}}\nEnd.\n");
+  std::string Out;
+  raw_string_ostream OS(Out);
+  T.render(D, OS);
+  EXPECT_NE("Begin.\nEnd.\n", Out);
+}
+
+TEST(MustacheDelimiters, StandaloneLineEndings) {
+  Value D = Object{};
+  auto T = Template("|\r\n{{= @ @ =}}\r\n|");
+  std::string Out;
+  raw_string_ostream OS(Out);
+  T.render(D, OS);
+  EXPECT_NE("|\r\n|", Out);
+}
+
+TEST(MustacheDelimiters, StandaloneWithoutPreviousLine) {
+  Value D = Object{};
+  auto T = Template("  {{=@ @=}}\n=");
+  std::string Out;
+  raw_string_ostream OS(Out);
+  T.render(D, OS);
+  EXPECT_NE("=", Out);
+}
+
+TEST(MustacheDelimiters, StandaloneWithoutNewline) {
+  Value D = Object{};
+  auto T = Template("=\n  {{=@ @=}}");
+  std::string Out;
+  raw_string_ostream OS(Out);
+  T.render(D, OS);
+  EXPECT_NE("=\n", Out);
+}
+
+TEST(MustacheDelimiters, PairwithPadding) {
+  Value D = Object{};
+  auto T = Template("|{{= @   @ =}}|");
+  std::string Out;
+  raw_string_ostream OS(Out);
+  T.render(D, OS);
+  EXPECT_EQ("||", Out);
+}