Index: clang-tools-extra/trunk/clang-tidy/utils/IncludeSorter.cpp
===================================================================
--- clang-tools-extra/trunk/clang-tidy/utils/IncludeSorter.cpp
+++ clang-tools-extra/trunk/clang-tidy/utils/IncludeSorter.cpp
@@ -61,7 +61,8 @@
                                       : IncludeSorter::IK_CXXSystemInclude;
   }
   StringRef CanonicalInclude = MakeCanonicalName(IncludeFile, Style);
-  if (CanonicalFile.equals(CanonicalInclude)) {
+  if (CanonicalFile.endswith(CanonicalInclude)
+      || CanonicalInclude.endswith(CanonicalFile)) {
     return IncludeSorter::IK_MainTUInclude;
   }
   if (Style == IncludeSorter::IS_Google) {
Index: clang-tools-extra/trunk/unittests/clang-tidy/IncludeInserterTest.cpp
===================================================================
--- clang-tools-extra/trunk/unittests/clang-tidy/IncludeInserterTest.cpp
+++ clang-tools-extra/trunk/unittests/clang-tidy/IncludeInserterTest.cpp
@@ -73,6 +73,17 @@
   bool IsAngledInclude() const override { return false; }
 };
 
+class EarlyInAlphabetHeaderInserterCheck : public IncludeInserterCheckBase {
+public:
+  EarlyInAlphabetHeaderInserterCheck(StringRef CheckName, ClangTidyContext *Context)
+      : IncludeInserterCheckBase(CheckName, Context) {}
+
+  std::vector<StringRef> HeadersToInclude() const override {
+    return {"a/header.h"};
+  }
+  bool IsAngledInclude() const override { return false; }
+};
+
 class MultipleHeaderInserterCheck : public IncludeInserterCheckBase {
 public:
   MultipleHeaderInserterCheck(StringRef CheckName, ClangTidyContext *Context)
@@ -114,6 +125,7 @@
                                        "insert_includes_test_header.h",
                                        "\n"},
                                       // Non system headers
+                                      {"a/header.h", "\n"},
                                       {"path/to/a/header.h", "\n"},
                                       {"path/to/z/header.h", "\n"},
                                       {"path/to/header.h", "\n"},
@@ -522,6 +534,77 @@
                                    "insert_includes_test_header.cc"));
 }
 
+TEST(IncludeInserterTest, DontInsertDuplicateIncludeEvenIfMiscategorized) {
+  const char *PreCode = R"(
+#include "clang_tidy/tests/insert_includes_test_header.h"
+
+#include <map>
+#include <set>
+#include <vector>
+
+#include "a/header.h"
+#include "path/to/a/header.h"
+#include "path/to/header.h"
+
+void foo() {
+  int a = 0;
+})";
+
+  const char *PostCode = R"(
+#include "clang_tidy/tests/insert_includes_test_header.h"
+
+#include <map>
+#include <set>
+#include <vector>
+
+#include "a/header.h"
+#include "path/to/a/header.h"
+#include "path/to/header.h"
+
+void foo() {
+  int a = 0;
+})";
+
+  EXPECT_EQ(PostCode, runCheckOnCode<EarlyInAlphabetHeaderInserterCheck>(
+                          PreCode, "workspace_folder/clang_tidy/tests/"
+                                   "insert_includes_test_header.cc"));
+}
+
+TEST(IncludeInserterTest, HandleOrderInSubdirectory) {
+  const char *PreCode = R"(
+#include "clang_tidy/tests/insert_includes_test_header.h"
+
+#include <map>
+#include <set>
+#include <vector>
+
+#include "path/to/a/header.h"
+#include "path/to/header.h"
+
+void foo() {
+  int a = 0;
+})";
+
+  const char *PostCode = R"(
+#include "clang_tidy/tests/insert_includes_test_header.h"
+
+#include <map>
+#include <set>
+#include <vector>
+
+#include "a/header.h"
+#include "path/to/a/header.h"
+#include "path/to/header.h"
+
+void foo() {
+  int a = 0;
+})";
+
+  EXPECT_EQ(PostCode, runCheckOnCode<EarlyInAlphabetHeaderInserterCheck>(
+                          PreCode, "workspace_folder/clang_tidy/tests/"
+                                   "insert_includes_test_header.cc"));
+}
+
 } // anonymous namespace
 } // namespace tidy
 } // namespace clang