diff --git a/materialyoucolor/temperature/temperature_cache.py b/materialyoucolor/temperature/temperature_cache.py
index 52c5de6..5c442a4 100644
--- a/materialyoucolor/temperature/temperature_cache.py
+++ b/materialyoucolor/temperature/temperature_cache.py
@@ -117,6 +117,13 @@ def complement(self) -> Hct:
         warmest_hue = self.warmest.hue
         warmest_temp = self.temps_by_hct.get(self.warmest, 0.0)
         range_temp = warmest_temp - coldest_temp
+
+        # At a tone extreme every hue resolves to the same color, leaving no range to
+        # divide by; return the input, as relative_temperature does in that case.
+        if range_temp == 0.0:
+            self.complement_cache = self.hcts_by_hue[round(self.input.hue)]
+            return self.complement_cache
+
         start_hue_is_coldest_to_warmest = TemperatureCache.is_between(
             self.input.hue, coldest_hue, warmest_hue
         )
diff --git a/tests/test_all.py b/tests/test_all.py
index 1d1d715..59637e5 100644
--- a/tests/test_all.py
+++ b/tests/test_all.py
@@ -19,6 +19,7 @@
 from materialyoucolor.scheme.scheme import Scheme
 from materialyoucolor.scheme.scheme_android import SchemeAndroid
 from materialyoucolor.score.score import Score
+from materialyoucolor.temperature.temperature_cache import TemperatureCache
 from materialyoucolor.utils.color_utils import hex_from_rgba, rgba_from_argb
 
 
@@ -119,6 +120,21 @@ def get_current_rss_mb():
 
 selected = Score.score(colors)
 
+
+# Regression: tone extremes leave TemperatureCache with a zero temperature range,
+# which used to make complement raise ZeroDivisionError (issue #28).
+def check_tone_extremes():
+    for argb in [0xFFFFFFFF, 0xFF000000, 0xFF010101]:
+        source = Hct.from_int(argb)
+        assert TemperatureCache(source).complement.to_int() == source.to_int()
+        for spec_version in ["2021", "2025"]:
+            for is_dark in [False, True]:
+                # SchemeFidelity reaches complement via get_tertiary_palette.
+                SchemeFidelity(source, is_dark, 0.0, spec_version=spec_version)
+
+
+check_tone_extremes()
+
 if os.name == "nt":
     exit(0)