diff --git a/src/scenarios/server/tools.ts b/src/scenarios/server/tools.ts
index 7ecbfdd5..5431be72 100644
--- a/src/scenarios/server/tools.ts
+++ b/src/scenarios/server/tools.ts
@@ -121,12 +121,20 @@ Implement tool \`test_simple_text\` with no arguments that returns:
       const connection = await connectToServer(serverUrl);
 
       const result = await connection.client.callTool({
-        name: 'test_simple_text'
-        /* omit arguments as it is not required in the schema */
+        name: 'test_simple_text',
+        // Per MCP spec, `arguments` is optional when the tool's inputSchema
+        // has no required fields. But the typescript-sdk server (<= 1.29.x)
+        // rejects undefined `arguments` against any inputSchema, returning
+        // isError: true. Fix merged into main (PR #1404) but not backported
+        // to the 1.x line — see modelcontextprotocol/typescript-sdk#1869.
+        // Passing `{}` explicitly until the fix is released.
+        arguments: {}
       });
 
       // Validate response
       const errors: string[] = [];
+      if ((result as any).isError === true)
+        errors.push('Tool returned an error instead of content');
       const content = (result as any).content;
       if (!content) errors.push('Missing content array');
       if (!Array.isArray(content)) errors.push('content is not an array');