diff --git a/ext/TensorKitMooncakeExt/indexmanipulations.jl b/ext/TensorKitMooncakeExt/indexmanipulations.jl
index 7c1bf833a..c3bc3e26c 100644
--- a/ext/TensorKitMooncakeExt/indexmanipulations.jl
+++ b/ext/TensorKitMooncakeExt/indexmanipulations.jl
@@ -281,10 +281,9 @@ for insertunit in (:insertleftunit, :insertrightunit)
             # sharing address spaces
             if tsrc isa TensorMap && !get(kwargs, :copy, false)
                 tsrc_cache = copy(tsrc)
-                tdst = $insertunit(tsrc, ival; kwargs...)
                 tdst_Δtdst = CoDual(
                     $insertunit(tsrc, ival; kwargs...),
-                    $insertunit(Mooncake.tangent(tsrc_Δtsrc), ival; kwargs...)
+                    $insertunit(Δtsrc, ival; kwargs...)
                 )
             else
                 tsrc_cache = nothing