diff --git a/src/pyrecest/filters/tracklet_viterbi.py b/src/pyrecest/filters/tracklet_viterbi.py
index 9c2318cfa..6d0e0a937 100644
--- a/src/pyrecest/filters/tracklet_viterbi.py
+++ b/src/pyrecest/filters/tracklet_viterbi.py
@@ -71,6 +71,13 @@ class TrackletAssociationCandidate:
     velocity: Any | None = None
     metadata: Mapping[str, Any] = field(default_factory=dict)
 
+    def __post_init__(self) -> None:
+        object.__setattr__(
+            self,
+            "unary_cost",
+            _as_scalar_float(self.unary_cost, "unary_cost"),
+        )
+
 
 @dataclass(frozen=True)
 class TrackletViterbiConfig:
@@ -283,12 +290,13 @@ def _solve_tracklet_viterbi(
                 for previous_miss_streak, previous_cost in state_costs[-1][
                     previous_index
                 ].items():
-                    transition_value = float(
+                    transition_value = _as_scalar_float(
                         transition(
                             previous_node.candidate,
                             current_node.candidate,
                             previous_miss_streak,
-                        )
+                        ),
+                        "transition_cost",
                     )
                     current_miss_streak = (
                         previous_miss_streak + 1 if current_node.is_miss else 0
diff --git a/tests/filters/test_tracklet_viterbi.py b/tests/filters/test_tracklet_viterbi.py
index 69f6f92d7..028edc4aa 100644
--- a/tests/filters/test_tracklet_viterbi.py
+++ b/tests/filters/test_tracklet_viterbi.py
@@ -268,3 +268,30 @@ def transition(previous, current, miss_streak):
         (1,),
         (2,),
     ]
+
+
+@pytest.mark.parametrize("invalid_cost", [np.nan, np.inf, -np.inf])
+def test_tracklet_candidate_rejects_nonfinite_unary_costs(invalid_cost):
+    with pytest.raises(ValueError, match="unary_cost must be finite"):
+        TrackletAssociationCandidate("invalid", unary_cost=invalid_cost)
+
+
+@pytest.mark.parametrize("invalid_cost", [np.nan, np.inf, -np.inf])
+def test_tracklet_viterbi_solvers_reject_nonfinite_transition_costs(invalid_cost):
+    frames = [
+        [TrackletAssociationCandidate("a", unary_cost=0.0)],
+        [TrackletAssociationCandidate("b", unary_cost=0.0)],
+    ]
+
+    def transition(_previous, _current, _miss_streak):
+        return invalid_cost
+
+    with pytest.raises(ValueError, match="transition_cost must be finite"):
+        solve_tracklet_viterbi(frames, transition_cost=transition)
+
+    with pytest.raises(ValueError, match="transition_cost must be finite"):
+        solve_fixed_lag_tracklet_viterbi(
+            frames,
+            lag_s=0.1,
+            transition_cost=transition,
+        )