diff --git a/mex/sources/libkorder/tl/symmetry.hh b/mex/sources/libkorder/tl/symmetry.hh
index 907b02c60..2aba4d9e6 100644
--- a/mex/sources/libkorder/tl/symmetry.hh
+++ b/mex/sources/libkorder/tl/symmetry.hh
@@ -127,7 +127,7 @@ public:
     return run;
   }
   [[nodiscard]] bool
-  operator==(const symiterator& it)
+  operator==(const symiterator& it) const
   {
     return dim == it.dim && run == it.run;
   }