diff --git a/lix/libexpr/primops.cc b/lix/libexpr/primops.cc
index b320987e0..91612bb4e 100644
--- a/lix/libexpr/primops.cc
+++ b/lix/libexpr/primops.cc
@@ -454,7 +454,12 @@ struct CompareValues : NeverAsync
         return (*this)(v1, v2, errorCtx);
     }
 
-    bool operator()(Value & v1, Value & v2, std::string_view errorCtx) const
+    bool operator()(Value const & v1, Value const & v2) const
+    {
+        return (*this)(v1, v2, errorCtx);
+    }
+
+    bool operator()(Value const & v1, Value const & v2, std::string_view errorCtx) const
     {
         try {
             if (v1.type() == nFloat && v2.type() == nInt) {