diff --git a/src/FormNetworks/abstractformnetwork.jl b/src/FormNetworks/abstractformnetwork.jl
index bb1b84be..8b6017c8 100644
--- a/src/FormNetworks/abstractformnetwork.jl
+++ b/src/FormNetworks/abstractformnetwork.jl
@@ -8,6 +8,7 @@ dual_index_map(f::AbstractFormNetwork) = not_implemented()
 tensornetwork(f::AbstractFormNetwork) = not_implemented()
 copy(f::AbstractFormNetwork) = not_implemented()
 derivative_vertices(f::AbstractFormNetwork) = not_implemented()
+bra_ket_vertices(f::AbstractFormNetwork, state_vertices::Vector) = not_implemented()
 
 bra(f::AbstractFormNetwork) = induced_subgraph(f, collect(values(bra_vertex_map(f))))
 ket(f::AbstractFormNetwork) = induced_subgraph(f, collect(values(ket_vertex_map(f))))
diff --git a/src/FormNetworks/quadraticformnetwork.jl b/src/FormNetworks/quadraticformnetwork.jl
index 11309bad..845fc26f 100644
--- a/src/FormNetworks/quadraticformnetwork.jl
+++ b/src/FormNetworks/quadraticformnetwork.jl
@@ -62,6 +62,10 @@ function QuadraticFormNetwork(
   return QuadraticFormNetwork(operator, ket; kwargs...)
 end
 
+function bra_ket_vertices(qf::QuadraticFormNetwork, state_vertices::Vector)
+  return vcat(bra_vertices(qf, state_vertices), ket_vertices(qf, state_vertices))
+end
+
 function update(qf::QuadraticFormNetwork, state_vertex, state::ITensor)
   qf = copy(qf)
   state_inds = inds(state)