diff --git a/mem0-ts/src/oss/src/prompts/index.ts b/mem0-ts/src/oss/src/prompts/index.ts
index c39ac25db..96cd762dd 100644
--- a/mem0-ts/src/oss/src/prompts/index.ts
+++ b/mem0-ts/src/oss/src/prompts/index.ts
@@ -31,6 +31,7 @@ export const MemoryUpdateSchema = z.object({
         old_memory: z
           .string()
           .optional()
+          .nullable()
           .describe(
             "The previous content of the memory item if the event was UPDATE.",
           ),