diff --git a/clang/lib/AST/RawCommentList.cpp b/clang/lib/AST/RawCommentList.cpp
--- a/clang/lib/AST/RawCommentList.cpp
+++ b/clang/lib/AST/RawCommentList.cpp
@@ -431,7 +431,7 @@
   };
 
   auto DropTrailingNewLines = [](std::string &Str) {
-    while (Str.back() == '\n')
+    while (!Str.empty() && Str.back() == '\n')
       Str.pop_back();
   };
 
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 +124,10 @@
   // clang-format on
 }
 
+TEST_F(CommentTextTest, WorksWithEmptyBlockComments) {
+  auto ExpectedOutput = "";
+  auto Formatted = formatComment(R"(/* */)");
+  EXPECT_EQ(ExpectedOutput, Formatted);
+}
+
 } // namespace clang