diff --git a/src/worker/prompt.ts b/src/worker/prompt.ts
index c9514f4..a964f83 100644
--- a/src/worker/prompt.ts
+++ b/src/worker/prompt.ts
@@ -49,7 +49,7 @@ export interface PromptTokenizer {
 }
 
 interface SliceableTensor {
-  slice(...slices: (number[] | null)[]): unknown;
+  slice(...slices: ((number | null)[] | null)[]): unknown;
 }
 
 const WRAPPED = Symbol("whisper-web-prompt-support");