diff --git a/CHANGELOG.md b/CHANGELOG.md
index b317b16c9..8a5fe34ad 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -999,6 +999,12 @@ and this project adheres to [Semantic Versioning](https://semver.org/).
 
 ### Changed
 
+- The multiple-shock time guards go through `require_positive` like the rest
+  of the library. They were written as `not t > 0.0`, which rejects NaN where
+  `t <= 0.0` would accept it, and that reason lived in a comment. The shared
+  validator says the same thing in the form the whole package uses, rejects
+  infinities too, and names the parameter that failed instead of both at once.
+
 - `phonometry.vibration` has three families, by who reads them.
   `vibration.structural` is the structural acoustics that feeds building
   prediction: mobility (ISO 7626), plate junctions, radiation efficiency,
diff --git a/src/phonometry/vibration/human/multiple_shock.py b/src/phonometry/vibration/human/multiple_shock.py
index d0e3f73cf..b0f9913c9 100644
--- a/src/phonometry/vibration/human/multiple_shock.py
+++ b/src/phonometry/vibration/human/multiple_shock.py
@@ -252,10 +252,8 @@ def daily_dose(dose: float, exposure_time: float, measurement_time: float) -> fl
         was measured (same unit as ``exposure_time``).
     :return: The daily dose :math:`D_{zd} = D_z (t_d/t_m)^{1/6}`, m/s2.
     """
-    # Negated ">" rather than "<=" on purpose: it rejects NaN as well, which
-    # the opposite operator would let through.
-    if not measurement_time > 0.0 or not exposure_time > 0.0:  # NOSONAR - NaN
-        raise ValueError("exposure_time and measurement_time must be positive.")
+    exposure_time = require_positive(exposure_time, "exposure_time")
+    measurement_time = require_positive(measurement_time, "measurement_time")
     return float(dose * (exposure_time / measurement_time) ** (1.0 / DOSE_EXPONENT))
 
 
@@ -358,9 +356,7 @@ def injury_risk(
     require_choice(sex, "sex", _SEXES)
     if years <= 0:
         raise ValueError("years must be a positive integer.")
-    # Negated ">" rather than "<=" on purpose: it rejects NaN as well.
-    if not days_per_year > 0.0:  # NOSONAR - NaN
-        raise ValueError("days_per_year must be positive.")
+    days_per_year = require_positive(days_per_year, "days_per_year")
     mz = _mz_for_sex(sex) if mz is None else mz
     s_stat = static_stress(mz)
     ages = start_age + np.arange(years, dtype=np.float64)
diff --git a/tests/vibration/human/test_multiple_shock_vibration.py b/tests/vibration/human/test_multiple_shock_vibration.py
index 5abd570b6..051e9c74a 100644
--- a/tests/vibration/human/test_multiple_shock_vibration.py
+++ b/tests/vibration/human/test_multiple_shock_vibration.py
@@ -230,11 +230,12 @@ def test_response_peaks_rejects_2d() -> None:
     with pytest.raises(ValueError, match="1-D time series"):
         v.response_peaks(np.zeros((2, 100)))
 
-def test_the_time_guards_reject_nan() -> None:
-    """``not t > 0`` is deliberate: ``t <= 0`` would let NaN through."""
-    with pytest.raises(ValueError, match="must be positive"):
-        v.daily_dose(1.0, exposure_time=math.nan, measurement_time=1.0)
-    with pytest.raises(ValueError, match="must be positive"):
-        v.daily_dose(1.0, exposure_time=1.0, measurement_time=math.nan)
-    with pytest.raises(ValueError, match="days_per_year must be positive"):
-        v.injury_risk(0.5, start_age=20.0, years=20, days_per_year=math.nan)
+def test_the_time_guards_reject_nan_and_infinity() -> None:
+    """The guards go through require_positive, which rejects both."""
+    for bad in (math.nan, math.inf):
+        with pytest.raises(ValueError, match="'exposure_time' must be positive"):
+            v.daily_dose(1.0, exposure_time=bad, measurement_time=1.0)
+        with pytest.raises(ValueError, match="'measurement_time' must be positive"):
+            v.daily_dose(1.0, exposure_time=1.0, measurement_time=bad)
+        with pytest.raises(ValueError, match="'days_per_year' must be positive"):
+            v.injury_risk(0.5, start_age=20.0, years=20, days_per_year=bad)