diff --git a/src/util/zygote_rules.jl b/src/util/zygote_rules.jl
index b52324b5..a0a7b9a6 100644
--- a/src/util/zygote_rules.jl
+++ b/src/util/zygote_rules.jl
@@ -253,7 +253,8 @@ function Zygote._pullback(
     ctx::AContext, ::Type{Symmetric}, X::StridedMatrix{<:Real}, uplo=:U,
 )
     function Symmetric_pullback(Δ)
-        return nothing, _symmetric_back(Δ, uplo), nothing
+        ΔX = Δ === nothing ? nothing : _symmetric_back(Δ, uplo)
+        return nothing, ΔX, nothing
     end
     return Symmetric(X, uplo), Symmetric_pullback
 end
diff --git a/test/models/lgssm.jl b/test/models/lgssm.jl
index c8de690a..fb426e6e 100644
--- a/test/models/lgssm.jl
+++ b/test/models/lgssm.jl
@@ -123,7 +123,6 @@ println("lgssm:")
             max_primal_allocs=10,
             max_forward_allocs=35,
             max_backward_allocs=50,
-            # check_allocs=false,
             check_allocs=storage.val isa SArrayStorage,
         )
     end
diff --git a/test/test_util.jl b/test/test_util.jl
index 94128636..2a80d485 100644
--- a/test/test_util.jl
+++ b/test/test_util.jl
@@ -418,21 +418,20 @@ function test_interface(
     x_val = rand(rng, x)
     y = conditional_rand(rng, conditional, x_val)
 
-    # @testset "rand" begin
-    #     @test length(y) == dim_out(conditional)
-    #     args = (conditional, x_val)
-    #     @code_warntype conditional_rand(y, args...)
-    #     check_infers && @inferred conditional_rand(rng, args...)
-    #     if check_adjoints
-    #         adjoint_test(
-    #             (f, x) -> conditional_rand(MersenneTwister(123456), f, x), args;
-    #             check_infers=check_infers, kwargs...,
-    #         )
-    #     end
-    #     if check_allocs
-    #         check_adjoint_allocations(conditional_rand, (rng, args...); kwargs...)
-    #     end
-    # end
+    @testset "rand" begin
+        @test length(y) == dim_out(conditional)
+        args = (conditional, x_val)
+        check_infers && @inferred conditional_rand(rng, args...)
+        if check_adjoints
+            adjoint_test(
+                (f, x) -> conditional_rand(MersenneTwister(123456), f, x), args;
+                check_infers=check_infers, kwargs...,
+            )
+        end
+        if check_allocs
+            check_adjoint_allocations(conditional_rand, (rng, args...); kwargs...)
+        end
+    end
 
     @testset "predict" begin
         @test predict(x, conditional) isa Gaussian
@@ -450,26 +449,26 @@ function test_interface(
         @test cov(pred_marg) isa Diagonal
     end
 
-    # @testset "posterior_and_lml" begin
-    #     args = (x, conditional, y)
-    #     @test posterior_and_lml(args...) isa Tuple{Gaussian, Real}
-    #     check_infers && @inferred posterior_and_lml(args...)
-    #     if check_adjoints
-    #         (Δx, Δlml) = rand_zygote_tangent(posterior_and_lml(args...))
-    #         ∂args = map(rand_tangent, args)
-    #         adjoint_test(posterior_and_lml, (Δx, Δlml), args, ∂args)
-    #         adjoint_test(posterior_and_lml, (Δx, nothing), args, ∂args)
-    #         adjoint_test(posterior_and_lml, (nothing, Δlml), args, ∂args)
-    #         adjoint_test(posterior_and_lml, (nothing, nothing), args, ∂args)
-    #     end
-    #     if check_allocs
-    #         (Δx, Δlml) = rand_zygote_tangent(posterior_and_lml(args...))
-    #         check_adjoint_allocations(posterior_and_lml, (Δx, Δlml), args; kwargs...)
-    #         check_adjoint_allocations(posterior_and_lml, (nothing, Δlml), args; kwargs...)
-    #         check_adjoint_allocations(posterior_and_lml, (Δx, nothing), args; kwargs...)
-    #         check_adjoint_allocations(posterior_and_lml, (nothing, nothing), args; kwargs...)
-    #     end
-    # end
+    @testset "posterior_and_lml" begin
+        args = (x, conditional, y)
+        @test posterior_and_lml(args...) isa Tuple{Gaussian, Real}
+        check_infers && @inferred posterior_and_lml(args...)
+        if check_adjoints
+            (Δx, Δlml) = rand_zygote_tangent(posterior_and_lml(args...))
+            ∂args = map(rand_tangent, args)
+            adjoint_test(posterior_and_lml, (Δx, Δlml), args, ∂args)
+            adjoint_test(posterior_and_lml, (Δx, nothing), args, ∂args)
+            adjoint_test(posterior_and_lml, (nothing, Δlml), args, ∂args)
+            adjoint_test(posterior_and_lml, (nothing, nothing), args, ∂args)
+        end
+        if check_allocs
+            (Δx, Δlml) = rand_zygote_tangent(posterior_and_lml(args...))
+            check_adjoint_allocations(posterior_and_lml, (Δx, Δlml), args; kwargs...)
+            check_adjoint_allocations(posterior_and_lml, (nothing, Δlml), args; kwargs...)
+            check_adjoint_allocations(posterior_and_lml, (Δx, nothing), args; kwargs...)
+            check_adjoint_allocations(posterior_and_lml, (nothing, nothing), args; kwargs...)
+        end
+    end
 end
 
 """