diff --git a/README.md b/README.md
index f94fea295..65d5c4681 100644
--- a/README.md
+++ b/README.md
@@ -48,7 +48,7 @@ GSD v2 solves all of these because it's not a prompt framework anymore — it's
 
 ### Migrating from v1
 
-> **Note:** A `ROADMAP.md` file is **required** for migration. If your project doesn't have one, you'll need to create it before running the migration command.
+> **Note:** Migration works best with a `ROADMAP.md` file for milestone structure. Without one, milestones are inferred from the `phases/` directory.
 
 If you have projects with `.planning` directories from the original Get Shit Done, you can migrate them to GSD-2's `.gsd` format:
 
diff --git a/src/resources/extensions/gsd/migrate/command.ts b/src/resources/extensions/gsd/migrate/command.ts
index 58fec1f1d..e80731c14 100644
--- a/src/resources/extensions/gsd/migrate/command.ts
+++ b/src/resources/extensions/gsd/migrate/command.ts
@@ -99,7 +99,7 @@ export async function handleMigrate(
       `Directory not found: ${sourcePath}\n\n` +
       'Migration converts a .planning/ directory (from older GSD versions) into .gsd/ format.\n' +
       'If you are starting a new project, use /gsd:new-project instead.\n' +
-      'If migrating, ensure the path contains a .planning/ directory with a ROADMAP.md file.',
+      'If migrating, ensure the path contains a .planning/ directory.',
       "error",
     );
     return;
diff --git a/src/resources/extensions/gsd/migrate/validator.ts b/src/resources/extensions/gsd/migrate/validator.ts
index 9325eea7f..2bbf44dfb 100644
--- a/src/resources/extensions/gsd/migrate/validator.ts
+++ b/src/resources/extensions/gsd/migrate/validator.ts
@@ -14,7 +14,7 @@ function issue(file: string, severity: ValidationSeverity, message: string): Val
 /**
  * Validate that a .planning directory has the minimum required structure.
  * Returns structured issues with severity levels:
- * - fatal: directory doesn't exist or ROADMAP.md missing (migration cannot proceed)
+ * - fatal: directory doesn't exist (migration cannot proceed)
  * - warning: optional files missing (migration can proceed with reduced data)
  */
 export async function validatePlanningDirectory(path: string): Promise<ValidationResult> {
@@ -26,12 +26,10 @@ export async function validatePlanningDirectory(path: string): Promise<Validatio
     return { valid: false, issues };
   }
 
-  // ROADMAP.md is required (fatal if missing)
+  // ROADMAP.md — warn if missing (transformer falls back to filesystem phases)
   if (!existsSync(join(path, 'ROADMAP.md'))) {
-    issues.push(issue('ROADMAP.md', 'fatal',
-      `ROADMAP.md is required for migration (expected at ${join(path, 'ROADMAP.md')}). ` +
-      'Migration converts a .planning/ directory into .gsd/ format. ' +
-      'If you are starting fresh, use /gsd:new-project instead.',
+    issues.push(issue('ROADMAP.md', 'warning',
+      'ROADMAP.md not found — milestone structure will be inferred from phases/ directory',
     ));
   }
 
diff --git a/src/resources/extensions/gsd/tests/migrate-parser.test.ts b/src/resources/extensions/gsd/tests/migrate-parser.test.ts
index da5a19491..f30499374 100644
--- a/src/resources/extensions/gsd/tests/migrate-parser.test.ts
+++ b/src/resources/extensions/gsd/tests/migrate-parser.test.ts
@@ -725,8 +725,8 @@ Another orphan.
     }
   }
 
-  // ─── Test 12: Validation — missing ROADMAP.md → fatal ─────────────────
-  console.log('\n=== Validation: missing ROADMAP.md → fatal ===');
+  // ─── Test 12: Validation — missing ROADMAP.md → warning (not fatal) ───
+  console.log('\n=== Validation: missing ROADMAP.md → warning (not fatal) ===');
   {
     const base = createFixtureBase();
     try {
@@ -736,10 +736,10 @@ Another orphan.
 
       const result = await validatePlanningDirectory(planning);
 
-      assertEq(result.valid, false, 'no roadmap: validation fails');
+      assertEq(result.valid, true, 'no roadmap: validation still passes');
       assert(
-        result.issues.some(i => i.severity === 'fatal' && i.file.includes('ROADMAP')),
-        'no roadmap: fatal issue mentions ROADMAP'
+        result.issues.some(i => i.severity === 'warning' && i.file.includes('ROADMAP')),
+        'no roadmap: warning issue mentions ROADMAP'
       );
     } finally {
       cleanup(base);
diff --git a/src/resources/extensions/gsd/tests/migrate-validator-parsers.test.ts b/src/resources/extensions/gsd/tests/migrate-validator-parsers.test.ts
index 6e9804e8e..fa5b149bd 100644
--- a/src/resources/extensions/gsd/tests/migrate-validator-parsers.test.ts
+++ b/src/resources/extensions/gsd/tests/migrate-validator-parsers.test.ts
@@ -211,15 +211,15 @@ async function main(): Promise<void> {
     }
   }
 
-  console.log('\n=== Validator: missing ROADMAP.md → fatal ===');
+  console.log('\n=== Validator: missing ROADMAP.md → warning (not fatal) ===');
   {
     const base = createFixtureBase();
     try {
       const planning = createPlanningDir(base);
       writeFileSync(join(planning, 'PROJECT.md'), SAMPLE_PROJECT);
       const result = await validatePlanningDirectory(planning);
-      assertEq(result.valid, false, 'no roadmap: validation fails');
-      assert(result.issues.some(i => i.severity === 'fatal' && i.file.includes('ROADMAP')), 'no roadmap: fatal issue mentions ROADMAP');
+      assertEq(result.valid, true, 'no roadmap: validation still passes');
+      assert(result.issues.some(i => i.severity === 'warning' && i.file.includes('ROADMAP')), 'no roadmap: warning issue mentions ROADMAP');
     } finally {
       cleanup(base);
     }