diff --git a/packages/core/src/tools/tool-registry.test.ts b/packages/core/src/tools/tool-registry.test.ts
index 666930020a..dea1748194 100644
--- a/packages/core/src/tools/tool-registry.test.ts
+++ b/packages/core/src/tools/tool-registry.test.ts
@@ -550,8 +550,9 @@ describe('ToolRegistry', () => {
       expect(result.error?.type).toBe(
         ToolErrorType.DISCOVERED_TOOL_EXECUTION_ERROR,
       );
+      expect(result.llmContent).toContain('<stdout>(empty)</stdout>');
       expect(result.llmContent).toContain(
-        '<output>Something went wrong</output>',
+        '<stderr>Something went wrong</stderr>',
       );
       expect(result.llmContent).toContain('<exit_code>1</exit_code>');
     });
diff --git a/packages/core/src/tools/tool-registry.ts b/packages/core/src/tools/tool-registry.ts
index 20f9a64571..680d1e98cf 100644
--- a/packages/core/src/tools/tool-registry.ts
+++ b/packages/core/src/tools/tool-registry.ts
@@ -104,7 +104,7 @@ class DiscoveredToolInvocation extends BaseToolInvocation<
     // if there is any error, non-zero exit code, signal, or stderr, return error details instead of stdout
     if (error || code !== 0 || signal || stderr) {
       const parts = [
-        `<output>${(stdout + stderr).trim() || '(empty)'}</output>`,
+        `<output>\n    <stdout>${stdout.trim() || '(empty)'}</stdout>\n    <stderr>${stderr.trim() || '(empty)'}</stderr>\n  </output>`,
       ];
       if (error) {
         parts.push(`<error>${error}</error>`);