diff --git a/src/client/index.ts b/src/client/index.ts
index e256b4ed..c3662b29 100644
--- a/src/client/index.ts
+++ b/src/client/index.ts
@@ -6,6 +6,7 @@ import {
   ClientNotification,
   ClientRequest,
   ClientResult,
+  CompatibilityCallToolResultSchema,
   CompleteRequest,
   CompleteResultSchema,
   EmptyResultSchema,
@@ -218,11 +219,12 @@ export class Client<
 
   async callTool(
     params: CallToolRequest["params"],
+    resultSchema: typeof CallToolResultSchema | typeof CompatibilityCallToolResultSchema = CallToolResultSchema,
     onprogress?: ProgressCallback,
   ) {
     return this.request(
       { method: "tools/call", params },
-      CallToolResultSchema,
+      resultSchema,
       onprogress,
     );
   }
diff --git a/src/shared/protocol.ts b/src/shared/protocol.ts
index fdb117ca..22d2503f 100644
--- a/src/shared/protocol.ts
+++ b/src/shared/protocol.ts
@@ -1,4 +1,4 @@
-import { AnyZodObject, ZodLiteral, ZodObject, z } from "zod";
+import { ZodLiteral, ZodObject, ZodType, z } from "zod";
 import {
   ErrorCode,
   JSONRPCError,
@@ -250,7 +250,7 @@ export class Protocol<
    *
    * Do not use this method to emit notifications! Use notification() instead.
    */
-  request<T extends AnyZodObject>(
+  request<T extends ZodType<object>>(
     request: SendRequestT,
     resultSchema: T,
     onprogress?: ProgressCallback,
diff --git a/src/types.ts b/src/types.ts
index caf05785..f932699e 100644
--- a/src/types.ts
+++ b/src/types.ts
@@ -722,6 +722,13 @@ export const CallToolResultSchema = ResultSchema.extend({
   isError: z.boolean(),
 });
 
+/**
+ * CallToolResultSchema extended with backwards compatibility to protocol version 2024-10-07.
+ */
+export const CompatibilityCallToolResultSchema = CallToolResultSchema.or(ResultSchema.extend({
+  toolResult: z.unknown(),
+}));
+
 /**
  * Used by the client to invoke a tool provided by the server.
  */
@@ -1054,6 +1061,7 @@ export const ServerResultSchema = z.union([
   ListResourceTemplatesResultSchema,
   ReadResourceResultSchema,
   CallToolResultSchema,
+  CompatibilityCallToolResultSchema,
   ListToolsResultSchema,
 ]);
 
@@ -1148,6 +1156,7 @@ export type Tool = z.infer<typeof ToolSchema>;
 export type ListToolsRequest = z.infer<typeof ListToolsRequestSchema>;
 export type ListToolsResult = z.infer<typeof ListToolsResultSchema>;
 export type CallToolResult = z.infer<typeof CallToolResultSchema>;
+export type CompatibilityCallToolResult = z.infer<typeof CompatibilityCallToolResultSchema>;
 export type CallToolRequest = z.infer<typeof CallToolRequestSchema>;
 export type ToolListChangedNotification = z.infer<
   typeof ToolListChangedNotificationSchema