diff --git a/src/ColumnImplementations.jl b/src/ColumnImplementations.jl
index a495b8e..b810a3e 100644
--- a/src/ColumnImplementations.jl
+++ b/src/ColumnImplementations.jl
@@ -57,18 +57,6 @@ struct DenseInjectiveFinColumn{V<:AbstractVector{Int}} <: Column{Int,Int}
   pc::InjectiveCache{Int, Int, VecMap{Int, Vector{Int}}}
 end
 
-# Compatibility hack to support unique_index
-function Columns.preimage(dom, c::DenseInjectiveFinColumn, y::Int, ::UnboxInjectiveFlag)
-  # @warn "using old convention for preimage of unique-indexed homomorphisms"
-  get(c.pc.inverse, y, 0)
-end
-
-function Columns.preimage_multi(dom, c::DenseInjectiveFinColumn, ys, ::UnboxInjectiveFlag)
-  # @warn "using old convention for preimage of unique-indexed homomorphisms"
-  view_with_default(c.pc.inverse, ys, DefaultVal{0})
-end
-
-
 """
 A column for a dict-backed unindexed hom with key type K
 """
@@ -122,19 +110,6 @@ struct DenseInjectiveColumn{T, V<:AbstractVector{T}} <: Column{Int,T}
   pc::InjectiveCache{Int,T,DictMap{T,Int,Dict{T,Int}}}
 end
 
-# Compatibility hack
-function Columns.preimage(dom, c::DenseInjectiveColumn{T}, y::T, ::UnboxInjectiveFlag) where {T}
-  # @warn "using old convention for preimage of unique-indexed attributes"
-  get(c.pc.inverse.d, y, 0)
-end
-
-function Columns.preimage_multi(dom, c::DenseInjectiveColumn, ys, ::UnboxInjectiveFlag)
-  # @warn "using old convention for preimage of unique-indexed attributes"
-  broadcast(ys) do y
-    get(c.pc.inverse.d, y, 0)
-  end
-end
-
 """
 A column for a dict-backed unindexed hom with key type K
 """
diff --git a/src/Columns.jl b/src/Columns.jl
index bf4d1d3..fd72598 100644
--- a/src/Columns.jl
+++ b/src/Columns.jl
@@ -1,7 +1,6 @@
 module Columns
 export Mapping, PreimageCache, preimage, preimage_multi, add_mapping!, remove_mapping!,
-  Column, preimage, preimage_multi, undefine!,
-  UnboxInjectiveFlag
+  Column, preimage, preimage_multi, undefine!
 
 using MLStyle
 using StructEquality
@@ -56,14 +55,6 @@ function Base.setindex!(c::Column, y, x)
   c.m[x] = y
 end
 
-# This is to maintain compatibility with old convention for unique_indexing
-struct UnboxInjectiveFlag end
-
-# This is overloaded for specific columns to enable the old convention
-preimage(dom, c::Column, y, ::UnboxInjectiveFlag) = preimage(dom, c, y)
-
-preimage_multi(dom, c::Column, ys, ::UnboxInjectiveFlag) = preimage_multi(dom, c, ys)
-
 preimage(dom, c::Column, y) = preimage(dom, c.m, c.pc, y)
 
 preimage_multi(dom, c::Column, ys) = preimage_multi(dom, c.m, c.pc, ys)
diff --git a/src/DenseACSets.jl b/src/DenseACSets.jl
index 32ff025..d39d2d5 100644
--- a/src/DenseACSets.jl
+++ b/src/DenseACSets.jl
@@ -401,12 +401,8 @@ end
   parts(acs, @ct dom(s, f))
 end
 
-@inline function ACSetInterface.incident(acs::SimpleACSet, part, f::Symbol; unbox_injective=true) 
-  if !unbox_injective
-    return preimage(dom_parts(acs, f), acs.subparts[f], part)
-  else
-    return preimage(dom_parts(acs, f), acs.subparts[f], part, UnboxInjectiveFlag())
-  end
+@inline function ACSetInterface.incident(acs::SimpleACSet, part, f::Symbol)
+  preimage(dom_parts(acs, f), acs.subparts[f], part)
 end 
 
 """
@@ -415,21 +411,20 @@ equivalent to concatenating the results of incident on each part, i.e.
 `[incident(G,1,:src), incident(G,2,:src)]`.
 """
 @inline function ACSetInterface.incident(acs::SimpleACSet, 
-    parts::Union{AbstractVector,UnitRange}, f::Symbol; unbox_injective=true) 
-  T = isempty(parts) ? Vector{Int} : typeof(incident(acs, first(parts), f; unbox_injective=unbox_injective))
-  res = T[incident(acs, part, f; unbox_injective=unbox_injective) for part in parts]
-  return res # FIXME: update preimage_multi to work on attrs for better performance
+    parts::Union{AbstractVector,UnitRange}, f::Symbol)
+  # FIXME: update preimage_multi to work on attrs for better performance
+  AbstractVector{Int}[incident(acs, part, f) for part in parts]
 end 
 
-@inline ACSetInterface.incident(acs::StructACSet{S}, ::Colon, f::Symbol; unbox_injective=true) where {S} =
-  _incident(acs, Val{S}, :, Val{f}, unbox_injective)
+@inline ACSetInterface.incident(acs::StructACSet{S}, ::Colon, f::Symbol) where {S} =
+  _incident(acs, Val{S}, :, Val{f})
 
-ACSetInterface.incident(acs::DynamicACSet, ::Colon, f::Symbol; unbox_injective=true) =
-  runtime(_incident, acs, acs.schema, :, f, unbox_injective)
+ACSetInterface.incident(acs::DynamicACSet, ::Colon, f::Symbol) =
+  runtime(_incident, acs, acs.schema, :, f)
 
-@ct_enable function _incident(acs::SimpleACSet, @ct(S), ::Colon, @ct(f), unbox_injective)
+@ct_enable function _incident(acs::SimpleACSet, @ct(S), ::Colon, @ct(f))
   @ct s = Schema(S)
-  incident(acs, parts(acs, @ct(codom(s, f))), @ct(f); unbox_injective)
+  incident(acs, parts(acs, @ct(codom(s, f))), @ct(f))
 end
 
 @inline ACSetInterface.set_subpart!(acs::StructACSet{S,Ts}, part::Int, f::Symbol, subpart) where {S,Ts} =
@@ -466,10 +461,10 @@ ACSetInterface.rem_part!(acs::DynamicACSet, type::Symbol, part::Int) =
   last_part = acs.parts[@ct ob]
 
   @ct_ctrl for hom in in_homs
-    incoming_to_part = copy(incident(acs, part, @ct hom; unbox_injective=false))
+    incoming_to_part = copy(incident(acs, part, @ct hom))
     clear_subpart!(acs, incoming_to_part, @ct hom)
 
-    incoming_to_last_part = copy(incident(acs, last_part, @ct hom; unbox_injective=false))
+    incoming_to_last_part = copy(incident(acs, last_part, @ct hom))
     set_subpart!(acs, incoming_to_last_part, (@ct hom), part)
   end
 
diff --git a/test/ACSets.jl b/test/ACSets.jl
index 573c77b..46b74f0 100644
--- a/test/ACSets.jl
+++ b/test/ACSets.jl
@@ -1,9 +1,11 @@
 module TestCSetDataStructures
 using Test
 
-using ACSets
+using StaticArrays: StaticVector
 using Tables
 
+using ACSets
+
 # Discrete dynamical systems
 ############################
 
@@ -271,7 +273,7 @@ SchSubset = BasicSchema([:Set,:Sub], [(:ι,:Sub,:Set)])
 
 @acset_type Subset(SchSubset, unique_index=[:ι])
 
-Base.in(x, X::Subset) = incident(X, x, :ι) != 0
+Base.in(x::Integer, X::Subset) = !isempty(incident(X, x, :ι))
 
 A = Subset()
 add_parts!(A, :Set, 2)
@@ -281,6 +283,9 @@ add_parts!(B, :Set, 2)
 add_part!(B, :Sub, ι=2)
 @test 1 ∈ A && 2 ∉ A
 @test 1 ∉ B && 2 ∈ B
+@test incident(A, :, :ι) == [[1], []]
+@test incident(B, :, :ι) == [[], [1]]
+
 rem_part!(A, :Set, 2)
 @test 1 ∈ A
 rem_part!(B, :Set, 1)
@@ -358,14 +363,15 @@ for lset_maker in lset_makers
   lset = lset_maker(Symbol)
   add_parts!(lset, :X, 2, label=[:foo, :bar])
   @test subpart(lset, :, :label) == [:foo, :bar]
-  @test incident(lset, :foo, :label) == 1
-  @test incident(lset, [:foo,:bar], :label) == [1,2]
-  @test incident(lset, :nonkey, :label) == 0
+  @test incident(lset, :foo, :label) isa StaticVector
+  @test incident(lset, :foo, :label) == [1]
+  @test incident(lset, [:foo,:bar], :label) == [[1],[2]]
+  @test isempty(incident(lset, :nonkey, :label))
 
   set_subpart!(lset, 1, :label, :baz)
   @test subpart(lset, 1, :label) == :baz
-  @test incident(lset, :baz, :label) == 1
-  @test incident(lset, :foo, :label) == 0
+  @test incident(lset, :baz, :label) == [1]
+  @test isempty(incident(lset, :foo, :label))
 
   @test_throws Exception set_subpart!(lset, 1, :label, :bar)
 end
diff --git a/test/Project.toml b/test/Project.toml
index fc25ddd..cd9e63f 100644
--- a/test/Project.toml
+++ b/test/Project.toml
@@ -1,5 +1,6 @@
 [deps]
 ACSets = "227ef7b5-1206-438b-ac65-934d6da304b8"
 JSONSchema = "7d188eb4-7ad8-530c-ae41-71a32a6d4692"
+StaticArrays = "90137ffa-7385-5640-81b9-e52037218182"
 Tables = "bd369af6-aec1-5ad0-b16a-f7cc5008161c"
 Test = "8dfed614-e22c-5e08-85e1-65c5234f0b40"