diff --git a/apps/api/src/app/activities/activities.service.ts b/apps/api/src/app/activities/activities.service.ts
index da3e99312..ef3839340 100644
--- a/apps/api/src/app/activities/activities.service.ts
+++ b/apps/api/src/app/activities/activities.service.ts
@@ -20,12 +20,12 @@ import {
   DATA_GATHERING_QUEUE_PRIORITY_HIGH,
   GATHER_ASSET_PROFILE_PROCESS_JOB_NAME,
   GATHER_ASSET_PROFILE_PROCESS_JOB_OPTIONS,
-  ghostfolioPrefix,
   TAG_ID_EXCLUDE_FROM_ANALYSIS
 } from '@ghostfolio/common/config';
 import {
   canDeleteAssetProfile,
-  getAssetProfileIdentifier
+  getAssetProfileIdentifier,
+  isValidCustomAssetProfileSymbol
 } from '@ghostfolio/common/helper';
 import {
   ActivitiesResponse,
@@ -48,7 +48,6 @@ import {
   Type as ActivityType
 } from '@prisma/client';
 import { Big } from 'big.js';
-import { isUUID } from 'class-validator';
 import { endOfToday, isAfter } from 'date-fns';
 import { groupBy, uniqBy } from 'lodash';
 import { randomUUID } from 'node:crypto';
@@ -204,10 +203,9 @@ export class ActivitiesService {
       let symbol: string;
 
       if (
-        data.SymbolProfile.connectOrCreate.create.symbol.startsWith(
-          `${ghostfolioPrefix}_`
-        ) ||
-        isUUID(data.SymbolProfile.connectOrCreate.create.symbol)
+        isValidCustomAssetProfileSymbol(
+          data.SymbolProfile.connectOrCreate.create.symbol
+        )
       ) {
         // Connect custom asset profile (clone)
         symbol = data.SymbolProfile.connectOrCreate.create.symbol;
diff --git a/apps/api/src/app/admin/admin.service.ts b/apps/api/src/app/admin/admin.service.ts
index 4c608e0fd..b7499b62f 100644
--- a/apps/api/src/app/admin/admin.service.ts
+++ b/apps/api/src/app/admin/admin.service.ts
@@ -7,6 +7,7 @@ import { PrismaService } from '@ghostfolio/api/services/prisma/prisma.service';
 import { PropertyService } from '@ghostfolio/api/services/property/property.service';
 import { SymbolProfileService } from '@ghostfolio/api/services/symbol-profile/symbol-profile.service';
 import {
+  ghostfolioPrefix,
   PROPERTY_CURRENCIES,
   PROPERTY_IS_READ_ONLY_MODE,
   PROPERTY_IS_USER_SIGNUP_ENABLED
@@ -14,7 +15,8 @@ import {
 import {
   applyAssetProfileOverrides,
   getAssetProfileIdentifier,
-  getCurrencyFromSymbol
+  getCurrencyFromSymbol,
+  hasGhostfolioPrefix
 } from '@ghostfolio/common/helper';
 import {
   AdminData,
@@ -63,6 +65,12 @@ export class AdminService {
   > {
     try {
       if (dataSource === 'MANUAL') {
+        if (!hasGhostfolioPrefix(symbol)) {
+          throw new BadRequestException(
+            `symbol "${symbol}" must start with the prefix "${ghostfolioPrefix}_" for the data source "${dataSource}"`
+          );
+        }
+
         return this.symbolProfileService.add({
           currency,
           dataSource,
diff --git a/apps/api/src/services/data-provider/data-provider.service.ts b/apps/api/src/services/data-provider/data-provider.service.ts
index 4c273f2da..6ef7bdcbd 100644
--- a/apps/api/src/services/data-provider/data-provider.service.ts
+++ b/apps/api/src/services/data-provider/data-provider.service.ts
@@ -9,6 +9,7 @@ import { PropertyService } from '@ghostfolio/api/services/property/property.serv
 import {
   DEFAULT_CURRENCY,
   DERIVED_CURRENCIES,
+  ghostfolioPrefix,
   PROPERTY_API_KEY_GHOSTFOLIO,
   PROPERTY_DATA_SOURCE_MAPPING
 } from '@ghostfolio/common/config';
@@ -21,6 +22,7 @@ import {
   getStartOfUtcDate,
   isCurrency,
   isDerivedCurrency,
+  isValidCustomAssetProfileSymbol,
   isValidSearchQuery
 } from '@ghostfolio/common/helper';
 import {
@@ -289,6 +291,15 @@ export class DataProviderService implements OnModuleInit {
           continue;
         }
 
+        if (
+          dataSource === DataSource.MANUAL &&
+          !isValidCustomAssetProfileSymbol(symbol)
+        ) {
+          throw new Error(
+            `${activityPath}.symbol "${symbol}" must be a UUID or start with the prefix "${ghostfolioPrefix}_" for the data source "${DataSource.MANUAL}"`
+          );
+        }
+
         let assetProfile: Partial<SymbolProfile> = { currency };
 
         try {
diff --git a/libs/common/src/lib/dtos/create-asset-profile-with-market-data.dto.ts b/libs/common/src/lib/dtos/create-asset-profile-with-market-data.dto.ts
index 60afcb558..e9b26a5b6 100644
--- a/libs/common/src/lib/dtos/create-asset-profile-with-market-data.dto.ts
+++ b/libs/common/src/lib/dtos/create-asset-profile-with-market-data.dto.ts
@@ -1,7 +1,8 @@
 import { MarketData } from '@ghostfolio/common/interfaces';
+import { IsCustomAssetProfileSymbolConstraint } from '@ghostfolio/common/validator-constraints/is-custom-asset-profile-symbol';
 
 import { DataSource } from '@prisma/client';
-import { IsArray, IsIn, IsOptional } from 'class-validator';
+import { IsArray, IsIn, IsOptional, Validate } from 'class-validator';
 
 import { CreateAssetProfileDto } from './create-asset-profile.dto';
 
@@ -14,4 +15,7 @@ export class CreateAssetProfileWithMarketDataDto extends CreateAssetProfileDto {
   @IsArray()
   @IsOptional()
   marketData?: MarketData[];
+
+  @Validate(IsCustomAssetProfileSymbolConstraint)
+  override symbol: string;
 }
diff --git a/libs/common/src/lib/helper.spec.ts b/libs/common/src/lib/helper.spec.ts
index 42441a619..669c42e32 100644
--- a/libs/common/src/lib/helper.spec.ts
+++ b/libs/common/src/lib/helper.spec.ts
@@ -10,7 +10,8 @@ import {
   isAccountExcluded,
   isCurrency,
   isCurrencySymbol,
-  isSplitRatio
+  isSplitRatio,
+  isValidCustomAssetProfileSymbol
 } from '@ghostfolio/common/helper';
 
 describe('Helper', () => {
@@ -326,4 +327,32 @@ describe('Helper', () => {
       );
     });
   });
+
+  describe('Is valid custom asset profile symbol', () => {
+    it('Empty symbol', () => {
+      expect(isValidCustomAssetProfileSymbol('')).toEqual(false);
+    });
+
+    it('Free-text symbol', () => {
+      expect(isValidCustomAssetProfileSymbol('Penthouse Apartment')).toEqual(
+        false
+      );
+    });
+
+    it('Stock symbol', () => {
+      expect(isValidCustomAssetProfileSymbol('AAPL')).toEqual(false);
+    });
+
+    it('Symbol with Ghostfolio prefix', () => {
+      expect(isValidCustomAssetProfileSymbol('GF_PENTHOUSE_APARTMENT')).toEqual(
+        true
+      );
+    });
+
+    it('UUID', () => {
+      expect(
+        isValidCustomAssetProfileSymbol('7e91b7d4-1430-4212-8380-289a06c9bbc1')
+      ).toEqual(true);
+    });
+  });
 });
diff --git a/libs/common/src/lib/helper.ts b/libs/common/src/lib/helper.ts
index 22f969d02..6c0d6ea45 100644
--- a/libs/common/src/lib/helper.ts
+++ b/libs/common/src/lib/helper.ts
@@ -8,7 +8,7 @@ import {
   SymbolProfile
 } from '@prisma/client';
 import { Big } from 'big.js';
-import { isISO4217CurrencyCode } from 'class-validator';
+import { isISO4217CurrencyCode, isUUID } from 'class-validator';
 import {
   getDate,
   getMonth,
@@ -41,6 +41,7 @@ import {
   DERIVED_CURRENCIES,
   ghostfolioFearAndGreedIndexSymbolCryptocurrencies,
   ghostfolioFearAndGreedIndexSymbolStocks,
+  ghostfolioPrefix,
   SEARCH_QUERY_MINIMUM_LENGTH,
   TAG_ID_EXCLUDE_FROM_ANALYSIS
 } from './config';
@@ -466,6 +467,14 @@ export function getYesterday() {
   return subDays(new Date(Date.UTC(year, month, day)), 1);
 }
 
+export function hasGhostfolioPrefix(aSymbol: string) {
+  if (!aSymbol) {
+    return false;
+  }
+
+  return aSymbol.startsWith(`${ghostfolioPrefix}_`);
+}
+
 export function interpolate(template: string, context: any) {
   return template?.replace(/[$]{([^}]+)}/g, (_, objectPath) => {
     const properties = objectPath.split('.');
@@ -548,6 +557,10 @@ export function isSplitRatio({
   );
 }
 
+export function isValidCustomAssetProfileSymbol(aSymbol: string) {
+  return hasGhostfolioPrefix(aSymbol) || isUUID(aSymbol);
+}
+
 export function isValidSearchQuery(aQuery: string) {
   return aQuery?.trim().length >= SEARCH_QUERY_MINIMUM_LENGTH;
 }
diff --git a/libs/common/src/lib/validator-constraints/is-custom-asset-profile-symbol.ts b/libs/common/src/lib/validator-constraints/is-custom-asset-profile-symbol.ts
new file mode 100644
index 000000000..ea6e8e97e
--- /dev/null
+++ b/libs/common/src/lib/validator-constraints/is-custom-asset-profile-symbol.ts
@@ -0,0 +1,18 @@
+import {
+  ValidatorConstraint,
+  ValidatorConstraintInterface
+} from 'class-validator';
+
+import { ghostfolioPrefix } from '../config';
+import { isValidCustomAssetProfileSymbol } from '../helper';
+
+@ValidatorConstraint({ name: 'isCustomAssetProfileSymbol' })
+export class IsCustomAssetProfileSymbolConstraint implements ValidatorConstraintInterface {
+  public defaultMessage() {
+    return `$property must be a UUID or start with the prefix "${ghostfolioPrefix}_"`;
+  }
+
+  public validate(aSymbol: string) {
+    return isValidCustomAssetProfileSymbol(aSymbol);
+  }
+}