diff --git a/src/services/airtable-field-mapper.ts b/src/services/airtable-field-mapper.ts
index 18bd6c8..593d6b5 100644
--- a/src/services/airtable-field-mapper.ts
+++ b/src/services/airtable-field-mapper.ts
@@ -16,10 +16,10 @@ import type { FieldTypeMapper, StandardFieldType } from '../types';
 // value is server-computed) but still safe to use as a filename source
 // because the computed value is stable and typically text-like.
 const FILENAME_SAFE_TYPES = [
+  'formula',
+  'number',
   'singleLineText',
   'singleSelect',
-  'number',
-  'formula',
 ] as const;
 
 const READ_ONLY_TYPES = [
diff --git a/src/services/seatable-field-mapper.ts b/src/services/seatable-field-mapper.ts
index 6e8b2e7..506e74f 100644
--- a/src/services/seatable-field-mapper.ts
+++ b/src/services/seatable-field-mapper.ts
@@ -18,11 +18,11 @@ import type { FieldTypeMapper, StandardFieldType } from '../types';
 // `formula` appear here AND in READ_ONLY_TYPES below: they're great
 // stable identifiers but the sync pipeline must not push to them.
 const FILENAME_SAFE_TYPES = [
-  'text',
-  'single-select',
-  'number',
   'auto-number',
   'formula',
+  'number',
+  'single-select',
+  'text',
 ] as const;
 
 const READ_ONLY_TYPES = [
diff --git a/src/types/field-types.types.ts b/src/types/field-types.types.ts
index 2bcc3ae..5e36723 100644
--- a/src/types/field-types.types.ts
+++ b/src/types/field-types.types.ts
@@ -83,14 +83,16 @@ export interface FieldTypeMapper {
   isSubfolderSafe(providerType: string): boolean;
 
   /**
-   * Returns all known provider-specific types that pass `isFilenameSafe`.
-   * Enables UIs to enumerate the whitelist without guessing.
+   * Returns all known provider-specific types that pass `isFilenameSafe`,
+   * sorted and deduplicated. Enables UIs to enumerate the whitelist without
+   * guessing.
    */
   getFilenameSafeTypes(): readonly string[];
 
   /**
-   * Returns all known provider-specific types that pass `isSubfolderSafe`.
-   * Used by settings-tab to filter the subfolder field dropdown.
+   * Returns all known provider-specific types that pass `isSubfolderSafe`,
+   * sorted and deduplicated. Used by settings-tab to filter the subfolder
+   * field dropdown.
    */
   getSubfolderSafeTypes(): readonly string[];
 
diff --git a/tests/services/airtable-field-mapper.test.ts b/tests/services/airtable-field-mapper.test.ts
index f8de47f..9bdab4f 100644
--- a/tests/services/airtable-field-mapper.test.ts
+++ b/tests/services/airtable-field-mapper.test.ts
@@ -294,10 +294,10 @@ describe('airtableFieldMapper', () => {
     it('should return exactly the 4 filename-safe types', () => {
       const types = airtableFieldMapper.getFilenameSafeTypes();
       expect(types).toEqual([
+        'formula',
+        'number',
         'singleLineText',
         'singleSelect',
-        'number',
-        'formula',
       ]);
     });
 
diff --git a/tests/services/seatable-field-mapper.test.ts b/tests/services/seatable-field-mapper.test.ts
index 50e4b21..9897f6c 100644
--- a/tests/services/seatable-field-mapper.test.ts
+++ b/tests/services/seatable-field-mapper.test.ts
@@ -252,11 +252,11 @@ describe('seatableFieldMapper', () => {
     it('should return exactly the 5 filename-safe types', () => {
       const types = seatableFieldMapper.getFilenameSafeTypes();
       expect(types).toEqual([
-        'text',
-        'single-select',
-        'number',
         'auto-number',
         'formula',
+        'number',
+        'single-select',
+        'text',
       ]);
     });