diff --git a/README.md b/README.md
index 692ce4d..7f66fe8 100644
--- a/README.md
+++ b/README.md
@@ -1022,7 +1022,10 @@ Règles modélisées :
    les bonus de CA des huit types autorisés (« A creature can also add any
    circumstance, deflection, dodge, insight, luck, morale, profane, and
    sacred bonuses to AC to its CMD » — bonus issus des buffs/conditions/
-   dons, défense totale et combat défensif inclus) et une créature au
+   dons, défense totale et combat défensif inclus), **toutes les pénalités de CA
+   (« Any penalties to a creature's AC also apply to its CMD » — pénalités sans
+   type comme grapplé −2 ou à plat ventre −4 contre la mêlée, la manœuvre
+   étant un jet d'attaque de mêlée)** et une créature au
    contact pris de dos ne ajoute pas son bonus de Dextérité (« A flat-footed
    creature does not add its Dexterity bonus to its CMD » — la pénalité de
    Dextérité, qui n'est pas un bonus, reste appliquée).
diff --git a/src/pf1e_simulator/combat.py b/src/pf1e_simulator/combat.py
index 8392dbf..6f392db 100644
--- a/src/pf1e_simulator/combat.py
+++ b/src/pf1e_simulator/combat.py
@@ -4192,11 +4192,20 @@ class CombatEngine:
         dex_mod = target.combatant.abilities.dex_mod
         if self.has_condition_flag(target, "denies_dex_to_ac"):
             dex_mod = min(0, dex_mod)
-        ac_bonuses = resolve_modifiers(
+        # PF1e (SRD Combat Maneuvers): "Any penalties to a creature's AC also
+        # apply to its CMD." — negative AC modifiers ride the CMD whatever
+        # their bonus type; only positive ones are restricted to the eight
+        # SRD-listed types.
+        ac_mods = [
             m
             for m in self._stat_modifiers(target, "ac")
-            if m.bonus_type in _CMD_AC_BONUS_TYPES
-        )
+            if m.bonus_type in _CMD_AC_BONUS_TYPES or m.value < 0
+        ]
+        # A combat maneuver is a melee attack roll (SRD: "Combat maneuvers are
+        # attack rolls"), so the prone defender's -4 melee AC penalty applies.
+        if self._has_condition_named(target, "prone"):
+            ac_mods.append(StatModifier(target="ac", value=-4))
+        ac_bonuses = resolve_modifiers(ac_mods)
         # defensive_ac_bonus (total defense / fight defensively) is a dodge
         # bonus and aid_ac_bonus a circumstance bonus to AC — both types the
         # SRD lets a creature add to its CMD.
diff --git a/tests/test_maneuvers.py b/tests/test_maneuvers.py
index 77655c1..f1a24e5 100644
--- a/tests/test_maneuvers.py
+++ b/tests/test_maneuvers.py
@@ -504,9 +504,10 @@ def test_cmd_adds_eligible_ac_bonus_types() -> None:
     assert engine._maneuver_cmd(buffed) == 12 + 4 + 2
 
 
-def test_cmd_ignores_non_ac_bonus_types() -> None:
-    # Enhancement/natural armor bonuses and untyped penalties are NOT added
-    # to CMD (only the eight SRD-listed AC bonus types are).
+def test_cmd_ignores_non_ac_bonus_types_keeps_penalties() -> None:
+    # Enhancement bonuses are NOT among the eight SRD-listed types — ignored.
+    # But "Any penalties to a creature's AC also apply to its CMD" (SRD
+    # Combat Maneuvers): the untyped -4 penalty rides the CMD.
     engine = make_engine([], [])
     state = _buffed(
         make_combatant("b"),
@@ -515,7 +516,28 @@ def test_cmd_ignores_non_ac_bonus_types() -> None:
             StatModifier(target="ac", value=-4),
         ),
     )
-    assert engine._maneuver_cmd(state) == 12
+    assert engine._maneuver_cmd(state) == 12 - 4
+
+
+def test_cmd_includes_prone_and_grappled_penalties() -> None:
+    # A maneuver is a melee attack roll, so the prone -4 melee AC penalty and
+    # the grappled -2 AC penalty both apply to CMD (SRD: "Any penalties to a
+    # creature's AC also apply to its CMD").
+    engine = make_engine([], [])
+    prone = make_state(make_combatant("p"), "p", (0, 0))
+    prone.active_conditions.append(
+        ActiveCondition(
+            condition=CONDITIONS_BY_NAME["prone"], rounds_left=1, source="test"
+        )
+    )
+    assert engine._maneuver_cmd(prone) == 12 - 4
+    grappled = make_state(make_combatant("g"), "p", (0, 1))
+    grappled.active_conditions.append(
+        ActiveCondition(
+            condition=CONDITIONS_BY_NAME["grappled"], rounds_left=1, source="test"
+        )
+    )
+    assert engine._maneuver_cmd(grappled) == 12 - 2
 
 
 def test_cmd_flat_footed_drops_dex_bonus_keeps_penalty() -> None: