diff --git a/src/command_line.cc b/src/command_line.cc
index 8436c708..e8669a8f 100644
--- a/src/command_line.cc
+++ b/src/command_line.cc
@@ -178,7 +178,7 @@ void PushBack(NonElidedVector<lsLocation>* result, optional<lsLocation> location
 }
 
 QueryFile* FindFile(QueryDatabase* db, const std::string& filename, QueryFileId* file_id) {
-  auto it = db->usr_to_file.find(filename);
+  auto it = db->usr_to_file.find(LowerPathIfCaseInsensitive(filename));
   if (it != db->usr_to_file.end()) {
     optional<QueryFile>& file = db->files[it->second.id];
     if (file) {
@@ -193,8 +193,7 @@ QueryFile* FindFile(QueryDatabase* db, const std::string& filename, QueryFileId*
 }
 
 QueryFile* FindFile(QueryDatabase* db, const std::string& filename) {
-  // TODO: consider calling NormalizePath here. It might add too much latency though.
-  auto it = db->usr_to_file.find(filename);
+  auto it = db->usr_to_file.find(LowerPathIfCaseInsensitive(filename));
   if (it != db->usr_to_file.end()) {
     optional<QueryFile>& file = db->files[it->second.id];
     if (file)
diff --git a/src/query.cc b/src/query.cc
index e5dd9859..f45d2e53 100644
--- a/src/query.cc
+++ b/src/query.cc
@@ -261,12 +261,12 @@ QueryFile::Def BuildFileDef(const IdMap& id_map, const IndexFile& indexed) {
 
 
 QueryFileId GetQueryFileIdFromPath(QueryDatabase* query_db, const std::string& path) {
-  auto it = query_db->usr_to_file.find(path);
+  auto it = query_db->usr_to_file.find(LowerPathIfCaseInsensitive(path));
   if (it != query_db->usr_to_file.end())
     return QueryFileId(it->second.id);
 
   size_t idx = query_db->files.size();
-  query_db->usr_to_file[path] = QueryFileId(idx);
+  query_db->usr_to_file[LowerPathIfCaseInsensitive(path)] = QueryFileId(idx);
   query_db->files.push_back(QueryFile(path));
   return QueryFileId(idx);
 }
@@ -625,7 +625,7 @@ void QueryDatabase::RemoveUsrs(SymbolKind usr_kind, const std::vector<Usr>& to_r
   switch (usr_kind) {
     case SymbolKind::File: {
       for (const Usr& usr : to_remove)
-        files[usr_to_file[usr].id] = nullopt;
+        files[usr_to_file[LowerPathIfCaseInsensitive(usr)].id] = nullopt;
       break;
     }
     case SymbolKind::Type: {
@@ -691,7 +691,7 @@ void QueryDatabase::ImportOrUpdate(const std::vector<QueryFile::DefUpdate>& upda
   // This function runs on the querydb thread.
 
   for (auto& def : updates) {
-    auto it = usr_to_file.find(def.path);
+    auto it = usr_to_file.find(LowerPathIfCaseInsensitive(def.path));
     assert(it != usr_to_file.end());
 
     optional<QueryFile>& existing = files[it->second.id];
diff --git a/src/query.h b/src/query.h
index 69b5314f..d66f67b2 100644
--- a/src/query.h
+++ b/src/query.h
@@ -281,6 +281,8 @@ struct QueryDatabase {
   std::vector<optional<QueryVar>> vars;
 
   // Lookup symbol based on a usr.
+  // NOTE: For usr_to_file make sure to call LowerPathIfCaseInsensitive on key.
+  // TODO: add type wrapper to enforce we call it
   spp::sparse_hash_map<Usr, QueryFileId> usr_to_file;
   spp::sparse_hash_map<Usr, QueryTypeId> usr_to_type;
   spp::sparse_hash_map<Usr, QueryFuncId> usr_to_func;
diff --git a/src/utils.cc b/src/utils.cc
index c2ae783a..a0e7fd50 100644
--- a/src/utils.cc
+++ b/src/utils.cc
@@ -95,6 +95,15 @@ std::vector<std::string> SplitString(const std::string& str, const std::string&
   return strings;
 }
 
+std::string LowerPathIfCaseInsensitive(const std::string& path) {
+  std::string result = path;
+#if defined(_WIN32)
+  for (size_t i = 0; i < result.size(); ++i)
+    result[i] = (char)tolower(result[i]);
+#endif
+  return result;
+}
+
 static void GetFilesInFolderHelper(
     std::string folder, bool recursive, std::string output_prefix, const std::function<void(const std::string&)>& handler) {
   tinydir_dir dir;
diff --git a/src/utils.h b/src/utils.h
index 70150991..929fa8eb 100644
--- a/src/utils.h
+++ b/src/utils.h
@@ -23,6 +23,8 @@ std::string ReplaceAll(const std::string& source, const std::string& from, const
 
 std::vector<std::string> SplitString(const std::string& str, const std::string& delimiter);
 
+std::string LowerPathIfCaseInsensitive(const std::string& path);
+
 template <typename TValues>
 std::string StringJoin(const TValues& values) {
   std::string result;