diff --git a/packages/server/src/server/mcp.ts b/packages/server/src/server/mcp.ts
index 316074e2d..a4bb8f846 100644
--- a/packages/server/src/server/mcp.ts
+++ b/packages/server/src/server/mcp.ts
@@ -166,15 +166,16 @@ export class McpServer {
         );
 
         this.server.setRequestHandler('tools/call', async (request, ctx): Promise<CallToolResult | CreateTaskResult> => {
-            try {
-                const tool = this._registeredTools[request.params.name];
-                if (!tool) {
-                    throw new ProtocolError(ProtocolErrorCode.InvalidParams, `Tool ${request.params.name} not found`);
-                }
-                if (!tool.enabled) {
-                    throw new ProtocolError(ProtocolErrorCode.InvalidParams, `Tool ${request.params.name} disabled`);
-                }
+            // Tool lookup errors are JSON-RPC errors, not tool errors
+            const tool = this._registeredTools[request.params.name];
+            if (!tool) {
+                throw new ProtocolError(ProtocolErrorCode.InvalidParams, `Tool ${request.params.name} not found`);
+            }
+            if (!tool.enabled) {
+                throw new ProtocolError(ProtocolErrorCode.InvalidParams, `Tool ${request.params.name} disabled`);
+            }
 
+            try {
                 const isTaskRequest = !!request.params.task;
                 const taskSupport = tool.execution?.taskSupport;
                 const isTaskHandler = 'createTask' in (tool.handler as AnyToolHandler<AnySchema>);
diff --git a/test/integration/test/server/mcp.test.ts b/test/integration/test/server/mcp.test.ts
index 091e4ac21..ce4072006 100644
--- a/test/integration/test/server/mcp.test.ts
+++ b/test/integration/test/server/mcp.test.ts
@@ -1837,25 +1837,17 @@ describe('Zod v4', () => {
 
             await Promise.all([client.connect(clientTransport), mcpServer.server.connect(serverTransport)]);
 
-            const result = await client.request(
-                {
-                    method: 'tools/call',
-                    params: {
-                        name: 'nonexistent-tool'
-                    }
-                },
-                CallToolResultSchema
-            );
-
-            expect(result.isError).toBe(true);
-            expect(result.content).toEqual(
-                expect.arrayContaining([
+            await expect(
+                client.request(
                     {
-                        type: 'text',
-                        text: expect.stringContaining('Tool nonexistent-tool not found')
-                    }
-                ])
-            );
+                        method: 'tools/call',
+                        params: {
+                            name: 'nonexistent-tool'
+                        }
+                    },
+                    CallToolResultSchema
+                )
+            ).rejects.toThrow(/Tool nonexistent-tool not found/);
         });
 
         /***