diff --git a/libnixf/include/nixf/Basic/Diagnostic.h b/libnixf/include/nixf/Basic/Diagnostic.h
index 6a4c28976..9ec1d9a6b 100644
--- a/libnixf/include/nixf/Basic/Diagnostic.h
+++ b/libnixf/include/nixf/Basic/Diagnostic.h
@@ -164,13 +164,13 @@ class Diagnostic : public PartialDiagnostic {
     return Notes.emplace_back(Kind, Range);
   }
 
-  std::vector<Note> &notes() { return Notes; }
+  [[nodiscard]] const std::vector<Note> &notes() const { return Notes; }
 
   Fix &fix(std::string Message) {
     return Fixes.emplace_back(Fix{{}, std::move(Message)});
   }
 
-  const std::vector<Fix> &fixes() { return Fixes; }
+  [[nodiscard]] const std::vector<Fix> &fixes() const { return Fixes; }
 
   [[nodiscard]] RangeTy range() const { return Range; }