diff --git a/lib/OptimizationLBFGSB/src/OptimizationLBFGSB.jl b/lib/OptimizationLBFGSB/src/OptimizationLBFGSB.jl
index 8dd2164e5d..6c5b95c89b 100644
--- a/lib/OptimizationLBFGSB/src/OptimizationLBFGSB.jl
+++ b/lib/OptimizationLBFGSB/src/OptimizationLBFGSB.jl
@@ -90,8 +90,6 @@ end
 function SciMLBase.__solve(cache::OptimizationCache{O}) where {O <: LBFGSB}
     maxiters = OptimizationBase._check_and_convert_maxiters(cache.solver_args.maxiters)
 
-    local x
-
     solver_kwargs = __map_optimizer_args(cache, cache.opt; maxiters, cache.solver_args...)
 
     if !isnothing(cache.f.cons)
@@ -220,12 +218,12 @@ function SciMLBase.__solve(cache::OptimizationCache{O}) where {O <: LBFGSB}
             stats = stats, retcode = opt_ret
         )
     else
-        iter_count = Ref(0)
+        ub_iter_count = Ref(0)
         encountered_inf_nan = Ref(false)
 
-        _loss = function (θ)
+        ub_loss = function (θ)
             x = cache.f(θ, cache.p)
-            iter_count[] += 1
+            ub_iter_count[] += 1
             # Track if we encounter Inf/NaN values in the objective
             if !isfinite(x[1])
                 encountered_inf_nan[] = true
@@ -267,7 +265,7 @@ function SciMLBase.__solve(cache::OptimizationCache{O}) where {O <: LBFGSB}
         t0 = time()
 
         res = optimizer(
-            _loss, _grad!, cache.u0, bounds; m = cache.opt.m, solver_kwargs...
+            ub_loss, _grad!, cache.u0, bounds; m = cache.opt.m, solver_kwargs...
         )
 
         # Extract the task message from the result
diff --git a/lib/OptimizationLBFGSB/test/core_tests.jl b/lib/OptimizationLBFGSB/test/core_tests.jl
index fc0f76bc83..f372fe5e3d 100644
--- a/lib/OptimizationLBFGSB/test/core_tests.jl
+++ b/lib/OptimizationLBFGSB/test/core_tests.jl
@@ -95,4 +95,15 @@ import SciMLBase
         @test res_safe.u[1] < 0.0
         @test res_safe.u[1] > -0.5
     end
+
+    # Regression: unconstrained LBFGSB path must not box `x` / dual-branch
+    # `iter_count`/`_loss` into Core.Box (dynamic dispatch on every eval).
+    @testset "no Core.Box in unconstrained LBFGSB __solve" begin
+        optf_box = OptimizationFunction(rosenbrock, OptimizationBase.AutoForwardDiff())
+        prob_box = OptimizationProblem(optf_box, zeros(2))
+        cache_box = init(prob_box, OptimizationLBFGSB.LBFGSB())
+        src = only(code_typed(SciMLBase.__solve, (typeof(cache_box),)))[1]
+        nboxes = count(t -> t === Core.Box, something(src.ssavaluetypes, []))
+        @test nboxes == 0
+    end
 end