diff --git a/src/libexpr/attr-set.hh b/src/libexpr/attr-set.hh
index c90bb0633..ba798196d 100644
--- a/src/libexpr/attr-set.hh
+++ b/src/libexpr/attr-set.hh
@@ -189,7 +189,7 @@ public:
         bindings = newBindings;
     }
 
-    friend class ExprAttrs;
+    friend struct ExprAttrs;
 };
 
 }