diff --git a/src/cli/App.tsx b/src/cli/App.tsx
index eb8e56b..fbf559f 100644
--- a/src/cli/App.tsx
+++ b/src/cli/App.tsx
@@ -2,7 +2,7 @@
 
 import { existsSync, readFileSync, renameSync, writeFileSync } from "node:fs";
 import { homedir, tmpdir } from "node:os";
-import { join } from "node:path";
+import { join, relative } from "node:path";
 import { APIError, APIUserAbortError } from "@letta-ai/letta-client/core/error";
 import type {
   AgentState,
@@ -672,13 +672,16 @@ function getPlanModeReminder(): string {
   }
 
   const planFilePath = permissionMode.getPlanFilePath();
+  const applyPatchRelativePath = planFilePath
+    ? relative(process.cwd(), planFilePath).replace(/\\/g, "/")
+    : null;
 
   // Generate dynamic reminder with plan file path
   return `${SYSTEM_REMINDER_OPEN}
       Plan mode is active. The user indicated that they do not want you to execute yet -- you MUST NOT make any edits (with the exception of the plan file mentioned below), run any non-readonly tools (including changing configs or making commits), or otherwise make any changes to the system. This supersedes any other instructions you have received.
 
 ## Plan File Info:
-${planFilePath ? `No plan file exists yet. You should create your plan at ${planFilePath} using a write tool (e.g. Write, ApplyPatch, etc. depending on your toolset).` : "No plan file path assigned."}
+${planFilePath ? `No plan file exists yet. You should create your plan at ${planFilePath} using a write tool (e.g. Write, ApplyPatch, etc. depending on your toolset).\n${applyPatchRelativePath ? `If using apply_patch, use this exact relative patch path: ${applyPatchRelativePath}.` : ""}` : "No plan file path assigned."}
 
 You should build your plan incrementally by writing to or editing this file. NOTE that this is the only file you are allowed to edit - other than this you are only allowed to take READ-ONLY actions.
 
@@ -12030,6 +12033,10 @@ ${SYSTEM_REMINDER_CLOSE}
 
     // Generate plan file path
     const planFilePath = generatePlanFilePath();
+    const applyPatchRelativePath = relative(
+      process.cwd(),
+      planFilePath,
+    ).replace(/\\/g, "/");
 
     // Toggle plan mode on and store plan file path
     permissionMode.setMode("plan");
@@ -12049,7 +12056,8 @@ In plan mode, you should:
 
 Remember: DO NOT write or edit any files yet. This is a read-only exploration and planning phase.
 
-Plan file path: ${planFilePath}`;
+Plan file path: ${planFilePath}
+If using apply_patch, use this exact relative patch path: ${applyPatchRelativePath}`;
 
     const precomputedResult: ToolExecutionResult = {
       toolReturn,
diff --git a/src/permissions/checker.ts b/src/permissions/checker.ts
index eace845..5a8093d 100644
--- a/src/permissions/checker.ts
+++ b/src/permissions/checker.ts
@@ -1,7 +1,7 @@
 // src/permissions/checker.ts
 // Main permission checking logic
 
-import { resolve } from "node:path";
+import { relative, resolve } from "node:path";
 import { getCurrentAgentId } from "../agent/context";
 import { runPermissionRequestHooks } from "../hooks";
 import { canonicalToolName, isShellToolName } from "./canonical";
@@ -308,9 +308,15 @@ function checkPermissionForEngine(
     let reason = `Permission mode: ${currentMode}`;
     if (currentMode === "plan" && modeOverride === "deny") {
       const planFilePath = permissionMode.getPlanFilePath();
+      const applyPatchRelativePath = planFilePath
+        ? relative(workingDirectory, planFilePath).replace(/\\/g, "/")
+        : null;
       reason =
         `Plan mode is active. You can only use read-only tools (Read, Grep, Glob, etc.) and write to the plan file. ` +
         `Write your plan to: ${planFilePath || "(error: plan file path not configured)"}. ` +
+        (applyPatchRelativePath
+          ? `If using apply_patch, use this exact relative path in patch headers: ${applyPatchRelativePath}. `
+          : "") +
         `Use ExitPlanMode when your plan is ready for user approval.`;
     }
     traceEvent(trace, "mode-override", reason);
diff --git a/src/tests/permissions-mode.test.ts b/src/tests/permissions-mode.test.ts
index 84a6869..1557d8f 100644
--- a/src/tests/permissions-mode.test.ts
+++ b/src/tests/permissions-mode.test.ts
@@ -279,6 +279,35 @@ test("plan mode - denies Write", () => {
   expect(result.reason).toContain("Plan mode is active");
 });
 
+test("plan mode deny reason includes exact apply_patch relative path hint", () => {
+  permissionMode.setMode("plan");
+  const workingDirectory = join(homedir(), "dev", "repo");
+  const planPath = join(homedir(), ".letta", "plans", "unit-test-plan.md");
+  const expectedRelativePath = relative(workingDirectory, planPath).replace(
+    /\\/g,
+    "/",
+  );
+  permissionMode.setPlanFilePath(planPath);
+
+  const permissions: PermissionRules = {
+    allow: [],
+    deny: [],
+    ask: [],
+  };
+
+  const result = checkPermission(
+    "Write",
+    { file_path: "/tmp/test.txt" },
+    permissions,
+    workingDirectory,
+  );
+
+  expect(result.decision).toBe("deny");
+  expect(result.reason).toContain(
+    `If using apply_patch, use this exact relative path in patch headers: ${expectedRelativePath}.`,
+  );
+});
+
 test("plan mode - allows Write to plan markdown file", () => {
   permissionMode.setMode("plan");
 
diff --git a/src/tools/impl/EnterPlanMode.ts b/src/tools/impl/EnterPlanMode.ts
index b644c89..6624ae3 100644
--- a/src/tools/impl/EnterPlanMode.ts
+++ b/src/tools/impl/EnterPlanMode.ts
@@ -1,3 +1,4 @@
+import { relative } from "node:path";
 import { generatePlanFilePath } from "../../cli/helpers/planName";
 import { permissionMode } from "../../permissions/mode";
 
@@ -26,6 +27,10 @@ export async function enter_plan_mode(
   }
 
   const planFilePath = permissionMode.getPlanFilePath();
+  const cwd = process.env.USER_CWD || process.cwd();
+  const applyPatchRelativePath = planFilePath
+    ? relative(cwd, planFilePath).replace(/\\/g, "/")
+    : null;
 
   return {
     message: `Entered plan mode. You should now focus on exploring the codebase and designing an implementation approach.
@@ -40,6 +45,7 @@ In plan mode, you should:
 
 Remember: DO NOT write or edit any files yet. This is a read-only exploration and planning phase.
 
-Plan file path: ${planFilePath}`,
+Plan file path: ${planFilePath}
+${applyPatchRelativePath ? `If using apply_patch, use this exact relative patch path: ${applyPatchRelativePath}` : ""}`,
   };
 }