diff --git a/Project.toml b/Project.toml
index b6571756..469ed53c 100644
--- a/Project.toml
+++ b/Project.toml
@@ -1,6 +1,6 @@
 name = "QuantumInputOutput"
 uuid = "18f9eda6-924c-47c7-a881-996695cfd7c6"
-version = "0.4.1"
+version = "0.4.2"
 
 [deps]
 DataInterpolations = "82cc6244-b520-54b8-b5a6-8a565e85f1d0"
diff --git a/examples/03-1_beam-combiner__PRA2023_107-023715_fig2-fig3.jl b/examples/03-1_beam-combiner__PRA2023_107-023715_fig2-fig3.jl
index 709befb4..88ce932b 100644
--- a/examples/03-1_beam-combiner__PRA2023_107-023715_fig2-fig3.jl
+++ b/examples/03-1_beam-combiner__PRA2023_107-023715_fig2-fig3.jl
@@ -32,6 +32,7 @@ av1 = Destroy(h, :av_2, 4)
 
 ## symbolic parameters
 @variables γ::Real Δ::Real gu_1::Number gu_2::Number gv_1::Number
+nothing # hide
 
 # We use the symbolic operators and parameters to define the SLH triples and cascade them to obtain the Hamiltonian and Lindblad for the system. 
 
diff --git a/examples/04-2_two-sided-cavity_with-atom_coh-drive__cumulants.jl b/examples/04-2_two-sided-cavity_with-atom_coh-drive__cumulants.jl
index 59bfbc04..117fd513 100644
--- a/examples/04-2_two-sided-cavity_with-atom_coh-drive__cumulants.jl
+++ b/examples/04-2_two-sided-cavity_with-atom_coh-drive__cumulants.jl
@@ -136,9 +136,9 @@ p
 
 # In the following, we include $N=2$ two-level atoms in the cavity and simulate the transmission and reflection of a coherent Gaussian pulse with a mean photon number of $|\alpha|^2 = 1/10$. We assume that the atoms are on resonance with the cavity, i.e. $\Delta = \Delta_c = \Delta_a$.
 
-# Obtain the ModelingToolkit independent variable from a seed mean-field problem and
-# register the classical drive as a function of it (QuantumCumulants v0.5 convention).
-t = meanfield([a], -Δ*a'a, [a]).iv
+# Define the ModelingToolkit independent variable and register the classical drive as a
+# function of it.
+@independent_variables t
 @register_symbolic Et(tt)
 
 G_d_t = SLH(1, Et(t), 0)
diff --git a/examples/05-1_N-QDs_bidirectional-waveguide_coherent-pulse.jl b/examples/05-1_N-QDs_bidirectional-waveguide_coherent-pulse.jl
index 2a2c5c00..09b72af3 100644
--- a/examples/05-1_N-QDs_bidirectional-waveguide_coherent-pulse.jl
+++ b/examples/05-1_N-QDs_bidirectional-waveguide_coherent-pulse.jl
@@ -158,6 +158,7 @@ p
 lT = length(T)
 G2 = zeros(lT, lT) # transmission
 G2_ref = zeros(lT, lT) # reflection
+nothing # hide
 
 # Materialize the lazy `TimeDependentSum` to a concrete operator at each time, so the
 # quantum-regression products below give a plain operator usable as the solver's initial state.
diff --git a/examples/08-1_pulse-delay__simple.jl b/examples/08-1_pulse-delay__simple.jl
index a8ae33c9..ac01fe24 100644
--- a/examples/08-1_pulse-delay__simple.jl
+++ b/examples/08-1_pulse-delay__simple.jl
@@ -189,6 +189,7 @@ nothing # hide
 p_t_sym = [g_u, g_in, g_out, g_v, M_ls...]
 p_t_num = [gu_, gin_, gout_, gv_, M_t_ls...]
 dict_p_t_int = Dict(p_t_sym .=> p_t_num)
+nothing # hide
 
 # The interaction picture eliminates the delay cavity `d`, so the numeric operators live
 # on the two-mode basis `bu ⊗ bv` (with `ad` mapped to the identity). Build on that basis.
diff --git a/src/SLH.jl b/src/SLH.jl
index 4ab6bccb..65cea3b3 100644
--- a/src/SLH.jl
+++ b/src/SLH.jl
@@ -288,6 +288,14 @@ function ▷(G1::SLH{N}, G2::SLH{N}) where {N}
     return _build_slh(S_t, L_t, H_t, op_hint)
 end
 
+function ▷(::SLH{N1}, ::SLH{N2}) where {N1,N2}
+    throw(
+        DimensionMismatch(
+            "cannot cascade SLH systems with different numbers of ports: $N1 and $N2",
+        ),
+    )
+end
+
 ▷(a::SLH, b::SLH, c::SLH...) = ▷(a ▷ b, c...)
 
 """
diff --git a/test/test_SLH.jl b/test/test_SLH.jl
index dbf43ee5..1ac400e7 100644
--- a/test/test_SLH.jl
+++ b/test/test_SLH.jl
@@ -58,6 +58,22 @@ using Test
         @test iszero(simplify(jump_operator(G2)[1] - (gu'*au + √(γ)*c + gv'*av)))
     end
 
+    @testset "cascade port mismatch" begin
+        G_two_port = G_u ⊞ G_c
+        expected_message = "cannot cascade SLH systems with different numbers of ports: 1 and 2"
+
+        for compose in (▷, cascade)
+            exception = try
+                compose(G_u, G_two_port)
+                nothing
+            catch exception
+                exception
+            end
+            @test exception isa DimensionMismatch
+            @test exception.msg == expected_message
+        end
+    end
+
     @testset "simple_concatenate" begin
         G1 = SLH(1, gu'*au, 0)
         G2 = SLH(1, √(γ)*c, Δ*c'c)