diff --git a/yt/visualization/fixed_resolution.py b/yt/visualization/fixed_resolution.py
index 9e6d9685ae2..44b8c7f3100 100644
--- a/yt/visualization/fixed_resolution.py
+++ b/yt/visualization/fixed_resolution.py
@@ -26,11 +26,6 @@
 
 from .volume_rendering.api import off_axis_projection
 
-if sys.version_info >= (3, 11):
-    from typing import assert_never
-else:
-    from typing_extensions import assert_never
-
 if sys.version_info >= (3, 12):
     from typing import override
 else:
@@ -627,7 +622,9 @@ def _sanitize_radius(self, r: Quantity) -> unyt_quantity:
         ):
             return self.ds.quan(*r).to("code_length")
         else:
-            assert_never(r)
+            raise TypeError(
+                f"Got unparsable radius value {r!r}, expected a unyt_quantity-like)"
+            )
 
     def _get_bounds(self) -> tuple[float, float, float, float]:
         dx = dy = self.radius.item()