diff --git a/clang-tools-extra/clangd/Headers.cpp b/clang-tools-extra/clangd/Headers.cpp
--- a/clang-tools-extra/clangd/Headers.cpp
+++ b/clang-tools-extra/clangd/Headers.cpp
@@ -193,8 +193,10 @@
   bool IsSystem = false;
   if (!HeaderSearchInfo)
     return "\"" + InsertedHeader.File + "\"";
-  std::string Suggested = HeaderSearchInfo->suggestPathToFileForDiagnostics(
-      InsertedHeader.File, BuildDir, &IsSystem);
+  // Suggest path might contain back slashes on windows.
+  std::string Suggested = llvm::sys::path::convert_to_slash(
+      HeaderSearchInfo->suggestPathToFileForDiagnostics(InsertedHeader.File,
+                                                        BuildDir, &IsSystem));
   if (IsSystem)
     Suggested = "<" + Suggested + ">";
   else