diff --git a/src/working_files.hh b/src/working_files.hh
index 1e3704b8..b95cd8fe 100644
--- a/src/working_files.hh
+++ b/src/working_files.hh
@@ -21,6 +21,7 @@ limitations under the License.
 #include <mutex>
 #include <optional>
 #include <string>
+#include <unordered_map>
 
 namespace ccls {
 struct WorkingFile {