diff --git a/dtypes.py b/dtypes.py
index 2be6a50..be3e1ff 100644
--- a/dtypes.py
+++ b/dtypes.py
@@ -101,8 +101,8 @@ def get_or_register_dtype(
 
         return dtype
 
-    def dtype_to_ctype(self, dtype: DTypeLike | None) -> str:
-        if dtype is None:
+    def dtype_to_ctype(self, dtype: DTypeLike) -> str:
+        if dtype is None:  # pyright: ignore[reportUnnecessaryComparison]
             raise ValueError("dtype may not be None")
 
         dtype = np.dtype(dtype)