diff --git a/packages/core/src/tools/exitPlanMode.test.ts b/packages/core/src/tools/exitPlanMode.test.ts
index 39f19babe97..a6f5c9cd8ac 100644
--- a/packages/core/src/tools/exitPlanMode.test.ts
+++ b/packages/core/src/tools/exitPlanMode.test.ts
@@ -57,6 +57,13 @@ describe('ExitPlanModeTool', () => {
       expect(tool.kind).toBe('think');
     });
 
+    // Regression for #5210: must stay declared so the model can call it
+    // directly in plan mode.
+    it('is always declared even though categorised as deferred (#5210)', () => {
+      expect(tool.shouldDefer).toBe(true);
+      expect(tool.alwaysLoad).toBe(true);
+    });
+
     it('should have correct schema', () => {
       expect(tool.schema).toEqual({
         name: 'exit_plan_mode',
diff --git a/packages/core/src/tools/exitPlanMode.ts b/packages/core/src/tools/exitPlanMode.ts
index 689b09b426f..a566cedc092 100644
--- a/packages/core/src/tools/exitPlanMode.ts
+++ b/packages/core/src/tools/exitPlanMode.ts
@@ -425,9 +425,10 @@ export class ExitPlanModeTool extends BaseDeclarativeTool<
       >,
       true, // isOutputMarkdown
       false, // canUpdateOutput
-      true, // shouldDefer — only used when leaving plan mode
-      false, // alwaysLoad
-      'plan mode exit approve',
+      true, // shouldDefer
+      // alwaysLoad: plan mode tells the model to call exit_plan_mode directly,
+      // so its schema must always be declared, not deferred (issue #5210).
+      true, // alwaysLoad
     );
   }
 
diff --git a/packages/core/src/tools/tool-registry.test.ts b/packages/core/src/tools/tool-registry.test.ts
index 9119708046d..815a746825a 100644
--- a/packages/core/src/tools/tool-registry.test.ts
+++ b/packages/core/src/tools/tool-registry.test.ts
@@ -11,6 +11,7 @@ import type { ConfigParameters } from '../config/config.js';
 import { Config, ApprovalMode } from '../config/config.js';
 import { ToolRegistry, DiscoveredTool } from './tool-registry.js';
 import { DiscoveredMCPTool } from './mcp-tool.js';
+import { ExitPlanModeTool } from './exitPlanMode.js';
 import type { FunctionDeclaration, CallableTool } from '@google/genai';
 import { mcpToTool } from '@google/genai';
 import { spawn } from 'node:child_process';
@@ -374,6 +375,20 @@ describe('ToolRegistry', () => {
       expect(names).toEqual(['always-visible']);
     });
 
+    // Regression for #5210: the real exit_plan_mode is deferred-category but
+    // must stay declared, otherwise the model cannot call it in plan mode.
+    it('keeps the real exit_plan_mode tool declared (#5210)', () => {
+      toolRegistry.registerTool(new ExitPlanModeTool(config));
+
+      const declared = toolRegistry
+        .getFunctionDeclarations()
+        .map((d) => d.name);
+      const deferred = toolRegistry.getDeferredToolSummary().map((t) => t.name);
+
+      expect(declared).toContain('exit_plan_mode');
+      expect(deferred).not.toContain('exit_plan_mode');
+    });
+
     it('includes revealed deferred tools in getFunctionDeclarations', () => {
       toolRegistry.registerTool(
         new MockTool({ name: 'hidden', shouldDefer: true }),