Index: lib/Format/Format.cpp
===================================================================
--- lib/Format/Format.cpp
+++ lib/Format/Format.cpp
@@ -1677,7 +1677,9 @@
   unsigned MinInsertOffset =
       getOffsetAfterHeaderGuardsAndComments(FileName, Code, Style);
   StringRef TrimmedCode = Code.drop_front(MinInsertOffset);
+  // Max insertion offset in the original code.
   unsigned MaxInsertOffset =
+      MinInsertOffset +
       getMaxHeaderInsertionOffset(FileName, TrimmedCode, Style);
   SmallVector<StringRef, 32> Lines;
   TrimmedCode.split(Lines, '\n');
Index: unittests/Format/CleanupTest.cpp
===================================================================
--- unittests/Format/CleanupTest.cpp
+++ unittests/Format/CleanupTest.cpp
@@ -916,6 +916,30 @@
   EXPECT_EQ(Expected, apply(Code, Replaces));
 }
 
+TEST_F(CleanUpReplacementsTest, LongCommentsInTheBeginningOfFile) {
+  std::string Code = "// Loooooooooooooooooooooooooong comment\n"
+                     "// Loooooooooooooooooooooooooong comment\n"
+                     "// Loooooooooooooooooooooooooong comment\n"
+                     "#include <string>\n"
+                     "#include <vector>\n"
+                     "\n"
+                     "#include \"a.h\"\n"
+                     "#include \"b.h\"\n";
+  std::string Expected = "// Loooooooooooooooooooooooooong comment\n"
+                         "// Loooooooooooooooooooooooooong comment\n"
+                         "// Loooooooooooooooooooooooooong comment\n"
+                         "#include <string>\n"
+                         "#include <vector>\n"
+                         "\n"
+                         "#include \"a.h\"\n"
+                         "#include \"b.h\"\n"
+                         "#include \"third.h\"\n";
+  tooling::Replacements Replaces =
+      toReplacements({createInsertion("#include \"third.h\"")});
+  Style = format::getGoogleStyle(format::FormatStyle::LanguageKind::LK_Cpp);
+  EXPECT_EQ(Expected, apply(Code, Replaces));
+}
+
 TEST_F(CleanUpReplacementsTest, CanDeleteAfterCode) {
   std::string Code = "#include \"a.h\"\n"
                      "void f() {}\n"