diff --git a/shared/sx/ref/run_continuation_tests.py b/shared/sx/ref/run_continuation_tests.py
index 8a7729e..1164266 100644
--- a/shared/sx/ref/run_continuation_tests.py
+++ b/shared/sx/ref/run_continuation_tests.py
@@ -35,8 +35,13 @@ finally:
 from shared.sx.parser import parse_all
 from shared.sx.types import NIL
 
-eval_expr = mod.eval_expr
-trampoline = mod.trampoline
+# Use tree-walk evaluator for interpreting .sx test files.
+# CEK is now the default, but test runners need tree-walk so that
+# transpiled HO forms (ho_map, etc.) don't re-enter CEK mid-evaluation.
+eval_expr = mod._tree_walk_eval_expr
+trampoline = mod._tree_walk_trampoline
+mod.eval_expr = eval_expr
+mod.trampoline = trampoline
 env = mod.make_env()
 
 # Platform test functions
diff --git a/shared/sx/ref/run_signal_tests.py b/shared/sx/ref/run_signal_tests.py
index 89a5eea..abcfb5d 100644
--- a/shared/sx/ref/run_signal_tests.py
+++ b/shared/sx/ref/run_signal_tests.py
@@ -14,8 +14,13 @@ sys.path.insert(0, _PROJECT)
 
 from shared.sx.parser import parse_all
 from shared.sx.ref import sx_ref
-from shared.sx.ref.sx_ref import eval_expr, trampoline, make_env, scope_push, scope_pop, sx_context
+from shared.sx.ref.sx_ref import make_env, scope_push, scope_pop, sx_context
 from shared.sx.types import NIL, Island, Lambda
+# Use tree-walk evaluator for interpreting .sx test files.
+eval_expr = sx_ref._tree_walk_eval_expr
+trampoline = sx_ref._tree_walk_trampoline
+sx_ref.eval_expr = eval_expr
+sx_ref.trampoline = trampoline
 
 # Build env with primitives
 env = make_env()
diff --git a/shared/sx/ref/run_type_tests.py b/shared/sx/ref/run_type_tests.py
index 8a63f0f..7ff2339 100644
--- a/shared/sx/ref/run_type_tests.py
+++ b/shared/sx/ref/run_type_tests.py
@@ -8,8 +8,16 @@ _PROJECT = os.path.abspath(os.path.join(_HERE, "..", "..", ".."))
 sys.path.insert(0, _PROJECT)
 
 from shared.sx.parser import parse_all
-from shared.sx.ref.sx_ref import eval_expr, trampoline, make_env, env_get, env_has, env_set
+from shared.sx.ref import sx_ref
+from shared.sx.ref.sx_ref import make_env, env_get, env_has, env_set
 from shared.sx.types import NIL, Component
+# Use tree-walk evaluator for interpreting .sx test files.
+# CEK is now the default, but the test runners need tree-walk so that
+# transpiled HO forms (ho_map, etc.) don't re-enter CEK mid-evaluation.
+eval_expr = sx_ref._tree_walk_eval_expr
+trampoline = sx_ref._tree_walk_trampoline
+sx_ref.eval_expr = eval_expr
+sx_ref.trampoline = trampoline
 
 # Build env with primitives
 env = make_env()