diff --git a/Project.toml b/Project.toml
index 724161b..20f8803 100644
--- a/Project.toml
+++ b/Project.toml
@@ -1,7 +1,7 @@
 name = "TensorAlgebra"
 uuid = "68bd88dc-f39d-4e12-b2ca-f046b68fcc6a"
 authors = ["ITensor developers <support@itensor.org> and contributors"]
-version = "0.3.7"
+version = "0.3.8"
 
 [deps]
 ArrayLayouts = "4c555306-a7a7-4459-81d9-ec55ddd5c99a"
diff --git a/src/contract/allocate_output.jl b/src/contract/allocate_output.jl
index 3fa1c02..bfaa7ef 100644
--- a/src/contract/allocate_output.jl
+++ b/src/contract/allocate_output.jl
@@ -1,5 +1,18 @@
 using Base.PermutedDimsArrays: genperm
 
+function check_input(::typeof(contract), a1, labels1, a2, labels2)
+  ndims(a1) == length(labels1) ||
+    throw(ArgumentError("Invalid permutation for left tensor"))
+  return ndims(a2) == length(labels2) ||
+         throw(ArgumentError("Invalid permutation for right tensor"))
+end
+
+function check_input(::typeof(contract), a_dest, labels_dest, a1, labels1, a2, labels2)
+  ndims(a_dest) == length(labels_dest) ||
+    throw(ArgumentError("Invalid permutation for destination tensor"))
+  return check_input(contract, a1, labels1, a2, labels2)
+end
+
 # TODO: Use `ArrayLayouts`-like `MulAdd` object,
 # i.e. `ContractAdd`?
 function output_axes(
@@ -28,6 +41,9 @@ function allocate_output(
   biperm2::AbstractBlockPermutation,
   α::Number=one(Bool),
 )
+  check_input(contract, a1, biperm1, a2, biperm2)
+  blocklengths(biperm_dest) == (length(biperm1[Block(1)]), length(biperm2[Block(2)])) ||
+    throw(ArgumentError("Invalid permutation for destination tensor"))
   axes_dest = output_axes(contract, biperm_dest, a1, biperm1, a2, biperm2, α)
   return similar(a1, promote_type(eltype(a1), eltype(a2), typeof(α)), axes_dest)
 end
diff --git a/src/contract/blockedperms.jl b/src/contract/blockedperms.jl
index a41033a..5f8d78c 100644
--- a/src/contract/blockedperms.jl
+++ b/src/contract/blockedperms.jl
@@ -8,6 +8,11 @@ end
 
 # codomain <-- domain
 function blockedperms(::typeof(contract), dimnames_dest, dimnames1, dimnames2)
+  dimnames = collect(Iterators.flatten((dimnames_dest, dimnames1, dimnames2)))
+  for i in unique(dimnames)
+    count(==(i), dimnames) == 2 || throw(ArgumentError("Invalid contraction labels"))
+  end
+
   codomain = Tuple(setdiff(dimnames1, dimnames2))
   contracted = Tuple(intersect(dimnames1, dimnames2))
   domain = Tuple(setdiff(dimnames2, dimnames1))
diff --git a/src/contract/contract.jl b/src/contract/contract.jl
index e47cc89..02665ca 100644
--- a/src/contract/contract.jl
+++ b/src/contract/contract.jl
@@ -88,6 +88,7 @@ function contract(
   α::Number=one(Bool);
   kwargs...,
 )
+  check_input(contract, a1, labels1, a2, labels2)
   biperm_dest, biperm1, biperm2 = blockedperms(contract, labels_dest, labels1, labels2)
   return contract(alg, biperm_dest, a1, biperm1, a2, biperm2, α; kwargs...)
 end
@@ -104,6 +105,7 @@ function contract!(
   β::Number;
   kwargs...,
 )
+  check_input(contract, a_dest, labels_dest, a1, labels1, a2, labels2)
   biperm_dest, biperm1, biperm2 = blockedperms(contract, labels_dest, labels1, labels2)
   return contract!(alg, a_dest, biperm_dest, a1, biperm1, a2, biperm2, α, β; kwargs...)
 end
@@ -118,6 +120,7 @@ function contract(
   α::Number;
   kwargs...,
 )
+  check_input(contract, a1, biperm1, a2, biperm2)
   a_dest = allocate_output(contract, biperm_dest, a1, biperm1, a2, biperm2, α)
   contract!(alg, a_dest, biperm_dest, a1, biperm1, a2, biperm2, α, zero(Bool); kwargs...)
   return a_dest
diff --git a/src/contract/contract_matricize/contract.jl b/src/contract/contract_matricize/contract.jl
index 98978bd..1bf6f70 100644
--- a/src/contract/contract_matricize/contract.jl
+++ b/src/contract/contract_matricize/contract.jl
@@ -11,6 +11,7 @@ function contract!(
   α::Number,
   β::Number,
 )
+  check_input(contract, a_dest, biperm_dest, a1, biperm1, a2, biperm2)
   a_dest_mat = matricize(a_dest, biperm_dest)
   a1_mat = matricize(a1, biperm1)
   a2_mat = matricize(a2, biperm2)
diff --git a/src/contract/output_labels.jl b/src/contract/output_labels.jl
index c2ffd6b..68525c5 100644
--- a/src/contract/output_labels.jl
+++ b/src/contract/output_labels.jl
@@ -10,10 +10,12 @@ function output_labels(
   return output_labels(f, alg, labels1, labels2)
 end
 
-function output_labels(f::typeof(contract), alg::Algorithm, labels1, labels2)
+function output_labels(f::typeof(contract), ::Algorithm, labels1, labels2)
   return output_labels(f, labels1, labels2)
 end
 
 function output_labels(::typeof(contract), labels1, labels2)
-  return Tuple(symdiff(labels1, labels2))
+  diff1 = Tuple(setdiff(labels1, labels2))
+  diff2 = Tuple(setdiff(labels2, labels1))
+  return tuplemortar((diff1, diff2))
 end
diff --git a/src/matricize.jl b/src/matricize.jl
index 666f058..85470a4 100644
--- a/src/matricize.jl
+++ b/src/matricize.jl
@@ -46,6 +46,7 @@ end
 # maybe: copy=false kwarg
 
 function matricize(a::AbstractArray, biperm::AbstractBlockPermutation{2})
+  ndims(a) == length(biperm) || throw(ArgumentError("Invalid bipermutation"))
   return matricize(FusionStyle(a), a, biperm)
 end
 
@@ -78,6 +79,7 @@ function unmatricize(
   axes::Tuple{Vararg{AbstractUnitRange}},
   biperm::AbstractBlockPermutation{2},
 )
+  length(axes) == length(biperm) || throw(ArgumentError("axes do not match permutation"))
   return unmatricize(FusionStyle(m), m, axes, biperm)
 end
 
@@ -122,6 +124,8 @@ end
 function unmatricize!(
   a::AbstractArray, m::AbstractMatrix, biperm::AbstractBlockPermutation{2}
 )
+  ndims(a) == length(biperm) ||
+    throw(ArgumentError("destination does not match permutation"))
   blocked_axes = axes(a)[biperm]
   a_perm = unmatricize(m, blocked_axes)
   return permuteblockeddims!(a, a_perm, invperm(biperm))
diff --git a/test/test_basics.jl b/test/test_basics.jl
index 53d48a9..26c52b9 100644
--- a/test/test_basics.jl
+++ b/test/test_basics.jl
@@ -5,6 +5,7 @@ using StableRNGs: StableRNG
 using TensorOperations: TensorOperations
 
 using TensorAlgebra:
+  BlockedTuple,
   blockedpermvcat,
   permuteblockeddims,
   permuteblockeddims!,
@@ -61,6 +62,7 @@ const elts = (Float32, Float64, Complex{Float32}, Complex{Float64})
 
     @test_throws MethodError matricize(a, (1, 2), (3,), (4,))
     @test_throws MethodError matricize(a, (1, 2, 3, 4))
+    @test_throws ArgumentError matricize(a, blockedpermvcat((1, 2), (3,)))
 
     v = ones(elt, 2)
     a_fused = matricize(v, (1,), ())
@@ -122,10 +124,23 @@ const elts = (Float32, Float64, Complex{Float32}, Complex{Float64})
     a = unmatricize(m, (), ())
     @test a isa Array{elt,0}
     @test a[] == m[1, 1]
+
+    @test_throws ArgumentError unmatricize(m, (), blockedpermvcat((1, 2), (3,)))
+    @test_throws ArgumentError unmatricize!(m, m, blockedpermvcat((1, 2), (3,)))
   end
 
   using TensorOperations: TensorOperations
   @testset "contract (eltype1=$elt1, eltype2=$elt2)" for elt1 in elts, elt2 in elts
+    elt_dest = promote_type(elt1, elt2)
+    a1 = ones(elt1, (1, 1))
+    a2 = ones(elt2, (1, 1))
+    a_dest = ones(elt_dest, (1, 1))
+    @test_throws ArgumentError contract(a1, (1, 2, 4), a2, (2, 3))
+    @test_throws ArgumentError contract(a1, (1, 2), a2, (2, 3, 4))
+    @test_throws ArgumentError contract((1, 3, 4), a1, (1, 2), a2, (2, 3))
+    @test_throws ArgumentError contract((1, 3), a1, (1, 2), a2, (2, 4))
+    @test_throws ArgumentError contract!(a_dest, (1, 3, 4), a1, (1, 2), a2, (2, 3))
+
     dims = (2, 3, 4, 5, 6, 7, 8, 9, 10)
     labels = (:a, :b, :c, :d, :e, :f, :g, :h, :i)
     for (d1s, d2s, d_dests) in (
@@ -155,8 +170,10 @@ const elts = (Float32, Float64, Complex{Float32}, Complex{Float64})
 
       # Don't specify destination labels
       a_dest, labels_dest′ = contract(a1, labels1, a2, labels2)
+      @test labels_dest′ isa
+        BlockedTuple{2,(length(setdiff(d1s, d2s)), length(setdiff(d2s, d1s)))}
       a_dest_tensoroperations = TensorOperations.tensorcontract(
-        labels_dest′, a1, labels1, a2, labels2
+        Tuple(labels_dest′), a1, labels1, a2, labels2
       )
       @test a_dest ≈ a_dest_tensoroperations
 
@@ -167,8 +184,18 @@ const elts = (Float32, Float64, Complex{Float32}, Complex{Float64})
       )
       @test a_dest ≈ a_dest_tensoroperations
 
+      # Specify with bituple
+      a_dest = contract(tuplemortar((labels_dest, ())), a1, labels1, a2, labels2)
+      @test a_dest ≈ a_dest_tensoroperations
+      a_dest = contract(tuplemortar(((), labels_dest)), a1, labels1, a2, labels2)
+      @test a_dest ≈ a_dest_tensoroperations
+      a_dest = contract(labels_dest′, a1, labels1, a2, labels2)
+      a_dest_tensoroperations = TensorOperations.tensorcontract(
+        Tuple(labels_dest′), a1, labels1, a2, labels2
+      )
+      @test a_dest ≈ a_dest_tensoroperations
+
       # Specify α and β
-      elt_dest = promote_type(elt1, elt2)
       # TODO: Using random `α`, `β` causing
       # random test failures, investigate why.
       α = elt_dest(1.2) # randn(elt_dest)
@@ -195,7 +222,7 @@ const elts = (Float32, Float64, Complex{Float32}, Complex{Float64})
     a2 = randn(rng, elt2, 4, 5)
 
     a_dest, labels = contract(a1, ("i", "j"), a2, ("k", "l"))
-    @test labels == ("i", "j", "k", "l")
+    @test labels == tuplemortar((("i", "j"), ("k", "l")))
     @test eltype(a_dest) === elt_dest
     @test a_dest ≈ reshape(vec(a1) * transpose(vec(a2)), (size(a1)..., size(a2)...))
 
@@ -225,17 +252,17 @@ const elts = (Float32, Float64, Complex{Float32}, Complex{Float64})
 
     # Array-scalar contraction.
     a_dest, labels_dest = contract(a, labels_a, s, ())
-    @test labels_dest == labels_a
+    @test labels_dest == tuplemortar((labels_a, ()))
     @test a_dest ≈ a * s[]
 
     # Scalar-array contraction.
     a_dest, labels_dest = contract(s, (), a, labels_a)
-    @test labels_dest == labels_a
+    @test labels_dest == tuplemortar(((), labels_a))
     @test a_dest ≈ a * s[]
 
     # Scalar-scalar contraction.
     a_dest, labels_dest = contract(s, (), t, ())
-    @test labels_dest == ()
+    @test labels_dest == tuplemortar(((), ()))
     @test a_dest[] ≈ s[] * t[]
 
     # Specify output labels.