diff --git a/clang/unittests/AST/CommentTextTest.cpp b/clang/unittests/AST/CommentTextTest.cpp
--- a/clang/unittests/AST/CommentTextTest.cpp
+++ b/clang/unittests/AST/CommentTextTest.cpp
@@ -124,4 +124,11 @@
   // clang-format on
 }
 
+TEST_F(CommentTextTest, EmptyFormattedText) {
+  // Test that empty formatted text doesn't cause crash.
+  const char *ExpectedOutput = "";
+  auto Formatted = formatComment("//!<");
+  EXPECT_EQ(ExpectedOutput, Formatted);
+}
+
 } // namespace clang