diff --git a/epymorph/engine/mm_exec.py b/epymorph/engine/mm_exec.py
index 278e1fc8..fe049d5e 100644
--- a/epymorph/engine/mm_exec.py
+++ b/epymorph/engine/mm_exec.py
@@ -114,23 +114,24 @@ def calculate_travelers(
 class StandardMovementExecutor(MovementEventsMixin, MovementExecutor):
     """The standard implementation of movement model execution."""
 
-    _ctx: MovementContext
     _model: MovementModel
-    _clause_masks: dict[TravelClause, NDArray[np.bool_]]
-    _predef: PredefData = {}
-    _predef_hash: int | None = None
+    _predef: PredefData
+    _predef_hash: int | None
+    _mobility: NDArray[np.bool_]
+    _ctx: MovementContext
 
     def __init__(
         self,
         ctx: MovementContext,
         mm: MovementSpec,
+        compartment_mobility: NDArray[np.bool_],
     ):
         MovementEventsMixin.__init__(self)
         self._model = compile_spec(mm, ctx.rng)
         self._predef = {}
         self._predef_hash = None
+        self._mobility = compartment_mobility
         self._ctx = ctx
-        self._clause_masks = {c: c.mask(ctx) for c in self._model.clauses}
         self._check_predef()
 
     def _check_predef(self) -> None:
@@ -141,8 +142,6 @@ def _check_predef(self) -> None:
                 self._predef = self._model.predef(self._ctx)
                 self._predef_hash = curr_hash
             except KeyError as e:
-                # NOTE: catching KeyError here will be necessary (to get nice error messages)
-                # until we can properly validate the MM clauses.
                 msg = f"Missing attribute {e} required by movement model predef."
                 raise AttributeException(msg) from None
 
@@ -167,7 +166,7 @@ def apply(self, world: World, tick: Tick) -> None:
 
             clause_event = calculate_travelers(
                 self._ctx, self._predef,
-                clause, self._clause_masks[clause], tick, local_array,
+                clause, self._mobility, tick, local_array,
             )
             self.on_movement_clause.publish(clause_event)
             travelers = clause_event.actual
diff --git a/epymorph/engine/standard_sim.py b/epymorph/engine/standard_sim.py
index cfbb8756..bbcea9c3 100644
--- a/epymorph/engine/standard_sim.py
+++ b/epymorph/engine/standard_sim.py
@@ -127,7 +127,17 @@ def run(self) -> Output:
 
         with error_gate("compiling the simulation", CompilationException):
             ipm_exec = StandardIpmExecutor(ctx, self.ipm)
-            movement_exec = StandardMovementExecutor(ctx, self.mm)
+
+            compartment_mobility = np.array(
+                ['immobile' not in tags for tags in self.ipm.compartment_tags],
+                dtype=np.bool_
+            )
+
+            movement_exec = StandardMovementExecutor(
+                ctx=ctx,
+                mm=self.mm,
+                compartment_mobility=compartment_mobility,
+            )
 
             # Proxy the movement_exec's events, if anyone is listening for them.
             if MovementEventsMixin.has_subscribers(self):
diff --git a/epymorph/movement/compile.py b/epymorph/movement/compile.py
index 9b51efab..f4187f52 100644
--- a/epymorph/movement/compile.py
+++ b/epymorph/movement/compile.py
@@ -126,10 +126,6 @@ def _compile_clause(
                 if d in clause.days
             )
 
-            # TODO: @cache?
-            def mask_predicate(ctx: MovementContext) -> NDArray[np.bool_]:
-                return ctx.compartment_mobility
-
             def move_predicate(_ctx: MovementContext, tick: Tick) -> bool:
                 return clause.leave_step == tick.step and \
                     tick.date.weekday() in clause_weekdays
@@ -142,7 +138,6 @@ def returns(_ctx: MovementContext, _tick: Tick) -> TickDelta:
 
             return DynamicTravelClause(
                 name=name_override(fn_ast.name),
-                mask_predicate=mask_predicate,
                 move_predicate=move_predicate,
                 requested=_adapt_move_function(fn, fn_ast),
                 returns=returns
diff --git a/epymorph/movement/movement_model.py b/epymorph/movement/movement_model.py
index 1b4f8087..a2e20f25 100644
--- a/epymorph/movement/movement_model.py
+++ b/epymorph/movement/movement_model.py
@@ -31,11 +31,6 @@ def geo(self) -> GeoData:
         """The geo data."""
         raise NotImplementedError
 
-    @property
-    def compartment_mobility(self) -> NDArray[np.bool_]:
-        """Which compartments from the IPM are subject to movement?"""
-        raise NotImplementedError
-
     @property
     def params(self) -> ParamsData:
         """The parameter data."""
@@ -64,10 +59,6 @@ class TravelClause(ABC):
 
     name: str
 
-    @abstractmethod
-    def mask(self, ctx: MovementContext) -> NDArray[np.bool_]:
-        """Calculate the movement mask for this clause."""
-
     @abstractmethod
     def predicate(self, ctx: MovementContext, tick: Tick) -> bool:
         """Should this clause apply this tick?"""
@@ -81,12 +72,6 @@ def returns(self, ctx: MovementContext, tick: Tick) -> TickDelta:
         """Calculate when this clause's movers should return (which may vary from tick-to-tick)."""
 
 
-MaskPredicate = Callable[[MovementContext], NDArray[np.bool_]]
-"""
-A predicate which creates a per-IPM-compartment mask:
-should this compartment be subject to movement by this clause?
-"""
-
 MovementPredicate = Callable[[MovementContext, Tick], bool]
 """A predicate which decides if a clause should fire this tick."""
 
@@ -108,26 +93,20 @@ class DynamicTravelClause(TravelClause):
 
     name: str
 
-    _mask: MaskPredicate
     _move: MovementPredicate
     _requested: MovementFunction
     _returns: ReturnsFunction
 
     def __init__(self,
                  name: str,
-                 mask_predicate: MaskPredicate,
                  move_predicate: MovementPredicate,
                  requested: MovementFunction,
                  returns: ReturnsFunction):
         self.name = name
-        self._mask = mask_predicate
         self._move = move_predicate
         self._requested = requested
         self._returns = returns
 
-    def mask(self, ctx: MovementContext) -> NDArray[np.bool_]:
-        return self._mask(ctx)
-
     def predicate(self, ctx: MovementContext, tick: Tick) -> bool:
         return self._move(ctx, tick)