diff --git a/.typos.toml b/.typos.toml
index 79b68a4..0d7bd16 100644
--- a/.typos.toml
+++ b/.typos.toml
@@ -1 +1,3 @@
-[default.extend-words]
\ No newline at end of file
+[default.extend-words]
+# Nd is the Modelica LimPID derivative-gain parameter name in the PID_Controller test fixture
+Nd = "Nd"
diff --git a/src/evaluator.jl b/src/evaluator.jl
index f389079..e8528ca 100644
--- a/src/evaluator.jl
+++ b/src/evaluator.jl
@@ -376,9 +376,14 @@ function eval_AST(when_eq::BaseModelicaWhenEquation)
             # Only fire on positive zero-crossing (condition becomes true) → Modelica edge semantics
             condition_sym = eval_when_rhs(condition_ast; in_body = false)
             crossing = to_zero_crossing(condition_sym)
+            # A when-condition is scalar, so `crossing ~ 0` is a single Equation.
+            # Annotate the literal as Equation[...] so it is always Vector{Equation}:
+            # without it inference admits a spurious Vector{Vector{Equation}} arm
+            # (crossing is a Union including a vector case) for which
+            # SymbolicContinuousCallback has no matching method.
             push!(
                 callbacks, ModelingToolkit.SymbolicContinuousCallback(
-                    [crossing ~ 0], affects;
+                    Equation[crossing ~ 0], affects;
                     affect_neg = nothing,
                     discrete_parameters = discrete_params_for_cb
                 )
@@ -766,7 +771,7 @@ function eval_AST(model::BaseModelicaModel)
                     modified = (; off = off_sym)
                 )
                 cb = ModelingToolkit.SymbolicContinuousCallback(
-                    [crossing ~ 0],
+                    Equation[crossing ~ 0],
                     affect;
                     affect_neg = affect_neg,
                     reinitializealg = BrownFullBasicInit(),
diff --git a/test/runtests.jl b/test/runtests.jl
index f30ce4a..66a23a3 100644
--- a/test/runtests.jl
+++ b/test/runtests.jl
@@ -23,7 +23,7 @@ run_tests(;
         @safetestset "ANTLR Parser Tests" include("test_antlr_parser.jl")
         return @safetestset "Error Message Tests" include("test_error_messages.jl")
     end,
-    groups = Dict("QA" => qa_group),
+    qa = qa_group,
     umbrellas = Dict("Quality" => ["QA"]),
     # Original runtests ran QA/Quality only for those explicit GROUPs, never under
     # "All"; curate "All" to Core only to preserve that.