diff --git a/src/build_function.jl b/src/build_function.jl
index 566455fb0..8dd03cf1a 100644
--- a/src/build_function.jl
+++ b/src/build_function.jl
@@ -102,21 +102,6 @@ function _build_and_inject_function(mod::Module, ex)
     RuntimeGeneratedFunctions.RuntimeGeneratedFunction(module_tag, module_tag, ex)
 end
 
-# Detect heterogeneous element types of "arrays of matrices/sparce matrices"
-function is_array_matrix(F)
-    return isa(F, AbstractVector) && all(x->isa(x, AbstractArray), F)
-end
-function is_array_sparse_matrix(F)
-    return isa(F, AbstractVector) && all(x->isa(x, AbstractSparseMatrix), F)
-end
-# Detect heterogeneous element types of "arrays of arrays of matrices/sparce matrices"
-function is_array_array_matrix(F)
-    return isa(F, AbstractVector) && all(x->isa(x, AbstractArray{<:AbstractMatrix}), F)
-end
-function is_array_array_sparse_matrix(F)
-    return isa(F, AbstractVector) && all(x->isa(x, AbstractArray{<:AbstractSparseMatrix}), F)
-end
-
 toexpr(n::Num, st) = toexpr(value(n), st)
 
 function fill_array_with_zero!(x::AbstractArray)
@@ -313,6 +298,10 @@ function set_array(s::MultithreadedForm, closed_args, out, outputidxs, rhss, che
     SpawnFetch{MultithreadedForm}(first.(arrays), last.(arrays), @inline noop(args...) = nothing)
 end
 
+function _set_array(out, outputidxs, rhss::AbstractSparseArray, checkbounds, skipzeros)
+    _set_array(LiteralExpr(:($out.nzval)), nothing, rhss.nzval, checkbounds, skipzeros)
+end
+
 function _set_array(out, outputidxs, rhss::AbstractArray, checkbounds, skipzeros)
     if outputidxs === nothing
         outputidxs = collect(eachindex(rhss))
diff --git a/test/build_function.jl b/test/build_function.jl
index 1113e0829..859791dfd 100644
--- a/test/build_function.jl
+++ b/test/build_function.jl
@@ -104,3 +104,15 @@ f = eval(build_function(sparse([1],[1], [(x+y)/k], 10,10), [x,y,k])[1])
 @test size(f([1.,1.,2])) == (10,10)
 @test f([1.,1.,2])[1,1] == 1.0
 @test sum(f([1.,1.,2])) == 1.0
+
+let # ModelingToolkit.jl#800
+    @variables x
+    y = sparse(1:3,1:3,x)
+
+    f1,f2 = build_function(y,x)
+    sf1, sf2 = string(f1), string(f2)
+    @test !contains(sf1, "CartesianIndex")
+    @test !contains(sf2, "CartesianIndex")
+    @test contains(sf1, "SparseMatrixCSC(")
+    @test contains(sf2, ".nzval")
+end