diff --git a/src/pyrecest/tracking/nonparametric_cardinality.py b/src/pyrecest/tracking/nonparametric_cardinality.py
index 8ef663f1fa..3f1ab61a10 100644
--- a/src/pyrecest/tracking/nonparametric_cardinality.py
+++ b/src/pyrecest/tracking/nonparametric_cardinality.py
@@ -10,10 +10,19 @@
 
 from dataclasses import dataclass
 from math import exp, isfinite, lgamma, log
-from numbers import Integral
+from numbers import Integral, Real
 from typing import Sequence
 
 
+def _as_finite_real_scalar(value, name: str) -> float:
+    if isinstance(value, bool) or not isinstance(value, Real):
+        raise TypeError(f"{name} must be a real scalar.")
+    value = float(value)
+    if not isfinite(value):
+        raise ValueError(f"{name} must be finite.")
+    return value
+
+
 @dataclass(frozen=True)
 class PitmanYorCardinalityPrior:
     """Pitman--Yor Chinese-restaurant prior over target-generated clusters.
@@ -48,12 +57,8 @@ class PitmanYorCardinalityPrior:
     discount: float = 0.0
 
     def __post_init__(self) -> None:
-        strength = float(self.strength)
-        discount = float(self.discount)
-        if not isfinite(strength):
-            raise ValueError("strength must be finite.")
-        if not isfinite(discount):
-            raise ValueError("discount must be finite.")
+        strength = _as_finite_real_scalar(self.strength, "strength")
+        discount = _as_finite_real_scalar(self.discount, "discount")
         if not 0.0 <= discount < 1.0:
             raise ValueError("discount must satisfy 0 <= discount < 1.")
         if strength <= -discount:
diff --git a/tests/tracking/test_nonparametric_cardinality.py b/tests/tracking/test_nonparametric_cardinality.py
index 397c90e9fb..630948f537 100644
--- a/tests/tracking/test_nonparametric_cardinality.py
+++ b/tests/tracking/test_nonparametric_cardinality.py
@@ -1,5 +1,6 @@
 import math
 
+import numpy as np
 import pytest
 
 from pyrecest.tracking.nonparametric_cardinality import (
@@ -81,6 +82,20 @@ def test_parameter_validation():
         DirichletProcessCardinalityPrior(strength=0.0)
 
 
+@pytest.mark.parametrize(
+    "kwargs",
+    [
+        pytest.param({"strength": True}, id="python-bool-strength"),
+        pytest.param({"strength": np.bool_(True)}, id="numpy-bool-strength"),
+        pytest.param({"discount": False}, id="python-bool-discount"),
+        pytest.param({"discount": np.bool_(False)}, id="numpy-bool-discount"),
+    ],
+)
+def test_parameter_validation_rejects_boolean_scalars(kwargs):
+    with pytest.raises(TypeError, match="must be a real scalar"):
+        PitmanYorCardinalityPrior(**kwargs)
+
+
 def test_cluster_size_validation():
     prior = PitmanYorCardinalityPrior()