diff --git a/ext/TensorKitChainRulesCoreExt/utility.jl b/ext/TensorKitChainRulesCoreExt/utility.jl
index 6896ff894..ef4afc3f8 100644
--- a/ext/TensorKitChainRulesCoreExt/utility.jl
+++ b/ext/TensorKitChainRulesCoreExt/utility.jl
@@ -24,3 +24,5 @@ function (::ProjectTo{DiagonalTensorMap{T, S, A}})(x::AbstractTensorMap) where {
     end
     return y
 end
+
+@non_differentiable TensorKit.degeneracystructure(::Any)