diff --git a/types/driftless/index.d.ts b/types/driftless/index.d.ts
index 00609df783..8fddd26dae 100644
--- a/types/driftless/index.d.ts
+++ b/types/driftless/index.d.ts
@@ -4,13 +4,13 @@
 // Definitions: https://github.com/DefinitelyTyped/DefinitelyTyped
 
 export function setDriftlessTimeout(
-    callback: (...args: any[]) => void,
+    callback: ((...args: any[]) => void) | string,
     delayMs: number,
     ...params: any[]
 ): number;
 
 export function setDriftlessInterval(
-    callback: (...args: any[]) => void,
+    callback: ((...args: any[]) => void) | string,
     delayMs: number,
     ...params: any[]
 ): number;