diff --git a/masque/builder/planner/planner.py b/masque/builder/planner/planner.py
index b684af9..f7c3cca 100644
--- a/masque/builder/planner/planner.py
+++ b/masque/builder/planner/planner.py
@@ -857,6 +857,22 @@ class Solver:
             return False
         return self.request.out_ptype is None or ptypes_compatible(end_port.ptype, self.request.out_ptype)
 
+    def rotation_matches_request(self, steps: Sequence[SelectedPrimitive]) -> bool:
+        """
+        Return true when a sequence can produce the requested output rotation.
+
+        Primitive parameters do not affect the rotation contract, so
+        rotation-impossible candidates can be rejected before parameter solving.
+        """
+        angle = 0.0
+        for step in steps:
+            step_rotation = step.out_port.rotation
+            if step_rotation is None:
+                raise BuildError('Primitive endpoints must have rotation')
+            angle += float(step_rotation) + pi
+        rotation_delta = ((angle - pi) - self.request.out_rotation) % (2 * pi)
+        return is_close(rotation_delta, 0) or is_close(rotation_delta, 2 * pi)
+
     def finalize(self, steps: Sequence[SelectedPrimitive]) -> Candidate:
         """
         Try all small solve sets for one raw sequence and return the first match.
@@ -874,6 +890,8 @@ class Solver:
                 raise BuildError(f'{self.request.route_name} route requires a jog constraint')
             constraints.append(('y', float(self.request.jog)))
         route_constraints = tuple(constraints)
+        if not self.rotation_matches_request(steps):
+            raise BuildError(f'{self.request.route_name} composed primitive route is unsupported')
         adjustable = self.adjustable_indices(steps)
         solve_sets: list[tuple[int, ...]] = [()]
         max_solve = min(len(route_constraints), len(adjustable))
diff --git a/masque/test/test_pather_primitive_offers.py b/masque/test/test_pather_primitive_offers.py
index ab8facf..06916ae 100644
--- a/masque/test/test_pather_primitive_offers.py
+++ b/masque/test/test_pather_primitive_offers.py
@@ -422,6 +422,53 @@ def test_pather_selects_lowest_cost_offer() -> None:
     assert numpy.allclose(p.ports['A'].offset, (-7, 0))
 
 
+def test_solver_rejects_rotation_impossible_candidates_before_parameter_solving() -> None:
+    invalid_parameters: list[float] = []
+
+    class RotationOfferTool(PlanningOnlyTool):
+        def primitive_offers(
+                self,
+                kind: Literal['straight', 'bend', 's', 'u'],
+                *,
+                in_ptype: str | None = None,
+                out_ptype: str | None = None,
+                **kwargs: Any,
+                ) -> tuple[PrimitiveOffer, ...]:
+            _ = kwargs
+            if kind != 'straight':
+                return ()
+
+            def invalid_endpoint(length: float) -> Port:
+                invalid_parameters.append(length)
+                return Port((length, 0), rotation=0, ptype=out_ptype or in_ptype)
+
+            def valid_endpoint(length: float) -> Port:
+                return Port((length, 0), rotation=pi, ptype=out_ptype or in_ptype)
+
+            return (
+                StraightOffer(
+                    in_ptype=in_ptype,
+                    out_ptype=out_ptype,
+                    endpoint_planner=invalid_endpoint,
+                    commit_planner=lambda length: {'kind': 'invalid', 'length': length},
+                    ),
+                StraightOffer(
+                    in_ptype=in_ptype,
+                    out_ptype=out_ptype,
+                    endpoint_planner=valid_endpoint,
+                    commit_planner=lambda length: {'kind': 'valid', 'length': length},
+                    ),
+                )
+
+    p = Pather(Library(), tools=RotationOfferTool(), auto_render=False)
+    p.ports['A'] = Port((0, 0), rotation=0, ptype='wire')
+
+    p.straight('A', 7)
+
+    assert p._paths['A'][0].data == {'kind': 'valid', 'length': 7}
+    assert invalid_parameters == [0.0, 0.0]
+
+
 def test_pather_commits_only_selected_offer() -> None:
     committed: list[str] = []