diff --git a/clang/lib/Tooling/Inclusions/HeaderIncludes.cpp b/clang/lib/Tooling/Inclusions/HeaderIncludes.cpp
--- a/clang/lib/Tooling/Inclusions/HeaderIncludes.cpp
+++ b/clang/lib/Tooling/Inclusions/HeaderIncludes.cpp
@@ -233,9 +233,6 @@
   return Ret;
 }
 bool IncludeCategoryManager::isMainHeader(StringRef IncludeName) const {
-  if (!IncludeName.startswith("\""))
-    return false;
-
   IncludeName =
       IncludeName.drop_front(1).drop_back(1); // remove the surrounding "" or <>
   // Not matchingStem: implementation files may have compound extensions but
@@ -259,8 +256,22 @@
   if (!Matching.empty()) {
     llvm::Regex MainIncludeRegex(HeaderStem.str() + Style.IncludeIsMainRegex,
                                  llvm::Regex::IgnoreCase);
-    if (MainIncludeRegex.match(Matching))
+    if (MainIncludeRegex.match(Matching)) {
+      // Matching is non-empty so these should be non-empty as well, making
+      // ++rbegin(IncludeName) and ++rbegin(FileName) safe.
+      assert(!IncludeName.empty());
+      assert(!FileName.empty());
+      // Checked stems above. Check remaining common path components here.
+      auto IncludePathRIter = ++llvm::sys::path::rbegin(IncludeName);
+      auto FilePathRiter = ++llvm::sys::path::rbegin(FileName);
+      for (; IncludePathRIter != llvm::sys::path::rend(IncludeName) &&
+             FilePathRiter != llvm::sys::path::rend(FileName);
+           ++IncludePathRIter, ++FilePathRiter) {
+        if (*IncludePathRIter != *FilePathRiter)
+          return false;
+      }
       return true;
+    }
   }
   return false;
 }
diff --git a/clang/unittests/Tooling/HeaderIncludesTest.cpp b/clang/unittests/Tooling/HeaderIncludesTest.cpp
--- a/clang/unittests/Tooling/HeaderIncludesTest.cpp
+++ b/clang/unittests/Tooling/HeaderIncludesTest.cpp
@@ -91,6 +91,28 @@
   EXPECT_EQ(Expected, insert(Code, "\"a.h\""));
 }
 
+TEST_F(HeaderIncludesTest, IsMainHeader) {
+  Style = format::getGoogleStyle(format::FormatStyle::LanguageKind::LK_Cpp)
+              .IncludeStyle;
+  std::vector<StringRef> FileNames{"foo/bar/baz.cpp", "foo/bar/baz.cu.cpp",
+                                   "foo/bar/baz_test.cu.cpp"};
+  for (const StringRef &FileName : FileNames) {
+    IncludeCategoryManager Manager(Style, FileName);
+    // These framework-style includes should all be considered "main".
+    EXPECT_EQ(Manager.getIncludePriority("<foo/bar/baz.h>", true), 0)
+        << "for source file " << FileName;
+    EXPECT_EQ(Manager.getIncludePriority("\"bar/baz.h\"", true), 0)
+        << "for source file " << FileName;
+    EXPECT_EQ(Manager.getIncludePriority("<baz.h>", true), 0)
+        << "for source file " << FileName;
+    // These should not be considered "main" as the paths to baz.h differ.
+    EXPECT_NE(Manager.getIncludePriority("<bar/foo/baz.h>", true), 0)
+        << "for source file " << FileName;
+    EXPECT_NE(Manager.getIncludePriority("\"foo/baz.h\"", true), 0)
+        << "for source file " << FileName;
+  }
+}
+
 TEST_F(HeaderIncludesTest, InsertAfterMainHeader) {
   std::string Code = "#include \"fix.h\"\n"
                      "\n"