diff --git a/src/pf1e_simulator/combat.py b/src/pf1e_simulator/combat.py
index 28b45a6..5ad1520 100644
--- a/src/pf1e_simulator/combat.py
+++ b/src/pf1e_simulator/combat.py
@@ -1064,7 +1064,7 @@ ACTION_RESULT_REASONS: frozenset[str] = frozenset({
     "downgraded:surprise",
     "delayed", "already_delayed", "ready",
     "not_prone", "already_prone", "unreachable_destination",
-    "weapon_unavailable", "invalid_destination",
+    "weapon_unavailable", "invalid_destination", "cannot_combine",
 })
 _REASON_OK = "ok"
 _REASON_UNSUPPORTED_KIND = "unsupported_kind"
@@ -1086,6 +1086,7 @@ _REASON_INVALID_DESTINATION = "invalid_destination"
 _REASON_NO_WEAPON = "no_weapon"
 _REASON_OUT_OF_RANGE = "out_of_range"
 _REASON_NO_LINE_OF_EFFECT = "no_line_of_effect"
+_REASON_CANNOT_COMBINE = "cannot_combine"
 
 # Action kinds that are declared but have no engine dispatch (U1 surfaces
 # them as explicit rejections instead of silent no-ops).
@@ -4115,10 +4116,14 @@ class CombatEngine:
         +4 dodge bonus to AC until the start of the combatant's next turn.
         PF1e (SRD "Total Defense"): "You can't make attacks of opportunity
         while using total defense" — the flag drops the AoO allowance to 0
-        (see ``_aoo_allowance``).
+        (see ``_aoo_allowance``) — and "You can't combine total defense with
+        fighting defensively": the bonus is SET (never stacked on a prior
+        +2) and a pending fighting-defensively declaration is voided (under
+        total defense no attack is made, so its -4 is moot).
         """
         state.total_defense = True
-        state.defensive_ac_bonus += _TOTAL_DEFENSE_AC_BONUS
+        state.fight_defensively = False
+        state.defensive_ac_bonus = _TOTAL_DEFENSE_AC_BONUS
         self._log(
             f"round {self._current_round} {state.combatant.id}: "
             f"total defense (+{_TOTAL_DEFENSE_AC_BONUS} AC)"
@@ -4129,7 +4134,18 @@ class CombatEngine:
         """Execute the fighting defensively action (PF1e): standard action
         granting a +2 dodge bonus to AC until the start of the combatant's
         next turn, at the cost of -4 on attack and crit confirmation rolls.
+        PF1e (SRD "Total Defense"): "You can't combine total defense with
+        fighting defensively" — the declaration is rejected while total
+        defense is active.
         """
+        if state.total_defense:
+            self._log(
+                f"round {self._current_round} {state.combatant.id}: "
+                f"fight_defensively rejected ({_REASON_CANNOT_COMBINE})"
+            )
+            return ActionResult(
+                kind="fight_defensively", ok=False, reason=_REASON_CANNOT_COMBINE
+            )
         state.fight_defensively = True
         state.defensive_ac_bonus += _FIGHT_DEFENSIVELY_AC_BONUS
         self._log(
diff --git a/tests/test_defensive_actions.py b/tests/test_defensive_actions.py
index 9f223f9..23cd276 100644
--- a/tests/test_defensive_actions.py
+++ b/tests/test_defensive_actions.py
@@ -256,3 +256,48 @@ def test_control_moving_foe_does_provoke_aoo() -> None:
     eng = _duel(moving_foe, [10, 5, 8, 3], round_cap=1)
     t = eng.run().transcript
     assert any("AoO vs foe" in line for line in t)
+
+
+# ── (g) total defense and fighting defensively do not stack ────────────────────
+
+
+def test_fight_defensively_rejected_while_total_defense_active() -> None:
+    # SRD "Total Defense": "You can't combine total defense with fighting
+    # defensively." Declaring it after total defense is rejected; the AC
+    # bonus stays exactly +4.
+    def policy(_engine: CombatEngine, state: CombatantState) -> tuple[Action, ...]:
+        if state.combatant.id == "hero":
+            return (
+                Action(kind="total_defense"),
+                Action(kind="fight_defensively"),
+            )
+        return _WAIT
+
+    eng = _duel(policy, [10, 5], round_cap=1)
+    t = eng.run().transcript
+    hero = eng._states[0]
+    assert "round 1 hero: fight_defensively rejected (cannot_combine)" in t
+    assert hero.defensive_ac_bonus == 4
+    assert hero.fight_defensively is False
+    assert ("fight_defensively", False, "cannot_combine") in tuple(
+        (r.kind, r.ok, r.reason) for r in hero.last_action_results
+    )
+
+
+def test_total_defense_supersedes_a_fighting_defensively_declaration() -> None:
+    # The reverse order: the +2 declaration is voided by the later total
+    # defense — the bonus is set to +4 (not +6) and the -4 attack flag clears.
+    def policy(_engine: CombatEngine, state: CombatantState) -> tuple[Action, ...]:
+        if state.combatant.id == "hero":
+            return (
+                Action(kind="fight_defensively"),
+                Action(kind="total_defense"),
+            )
+        return _WAIT
+
+    eng = _duel(policy, [10, 5], round_cap=1)
+    eng.run()
+    hero = eng._states[0]
+    assert hero.defensive_ac_bonus == 4
+    assert hero.fight_defensively is False
+    assert hero.total_defense is True