diff --git a/src/ACSetInterface.jl b/src/ACSetInterface.jl
index 41c2c5b..e78fda1 100644
--- a/src/ACSetInterface.jl
+++ b/src/ACSetInterface.jl
@@ -12,7 +12,6 @@ using Tables
 using PrettyTables: pretty_table
 
 using ..ColumnImplementations: AttrVar
-using ..PreimageCaches: is_injective
 
 using ..Schemas: types, attrs, attrtypes
 
@@ -251,9 +250,6 @@ function set_subpart! end
 # Inlined for the same reason as `subpart`.
 
 @inline function set_subpart!(acs::ACSet , parts::Union{AbstractVector{Int}, AbstractSet{Int}}, name, vals)
-  if is_injective(acs.subparts[name])
-    clear_subpart!(acs, parts, name)
-  end
   broadcast(parts, vals) do part, val
     set_subpart!(acs, part, name, val)
   end
diff --git a/src/Columns.jl b/src/Columns.jl
index bb0e1ea..fd72598 100644
--- a/src/Columns.jl
+++ b/src/Columns.jl
@@ -10,7 +10,7 @@ using Reexport
 @reexport using ..PreimageCaches
 
 import ..Mappings: view_with_default
-import ..PreimageCaches: preimage, preimage_multi, is_injective
+import ..PreimageCaches: preimage, preimage_multi
 
 # Columns
 #########
@@ -94,6 +94,4 @@ view_with_default(c::Column, xs, def) = ColumnView(c, xs, def)
 
 Base.size(c::ColumnView) = size(c.indices)
 
-is_injective(c::Column) = is_injective(c.pc)
-
 end
diff --git a/src/PreimageCaches.jl b/src/PreimageCaches.jl
index 7919084..205fe8a 100644
--- a/src/PreimageCaches.jl
+++ b/src/PreimageCaches.jl
@@ -35,7 +35,6 @@ performance implications.
 - [`preimage`](@ref)
 - [`assign!`](@ref)
 - [`unassign!`](@ref)
-- [`is_injective`](@ref) (defaults to false if not implemented)
 """
 abstract type PreimageCache{S,T} end
 
@@ -95,14 +94,6 @@ Remove `x` from the preimage of `y`.
 """
 function unassign! end
 
-"""
-Whether or not the cache imposes an injectivity constraint. (default: false)
-"""
-is_injective(::PreimageCache)::Bool = false
-
-# Caches
-########
-
 """
 The trivial preimage mapping. It just computes preimages on the fly, and the
 operations for updating it are noops
@@ -212,6 +203,4 @@ function unassign!(pc::InjectiveCache{S,T}, y::T, x::S) where {S,T}
   delete!(pc.inverse, y)
 end
 
-is_injective(::InjectiveCache)::Bool = true
-
 end
diff --git a/test/ACSets.jl b/test/ACSets.jl
index 2577bc0..b73e88b 100644
--- a/test/ACSets.jl
+++ b/test/ACSets.jl
@@ -425,8 +425,6 @@ for lset_maker in lset_makers
   @test isempty(incident(lset, :foo, :label))
 
   @test_throws Exception set_subpart!(lset, 1, :label, :bar)
-  set_subpart!(lset, :, :label, [:bar, :foo])
-  @test subpart(lset, :, :label) == [:bar, :foo]
 end
 
 SchDecGraph = BasicSchema([:E,:V], [(:src,:E,:V),(:tgt,:E,:V)],