diff --git a/packages/backend/server/src/base/error/def.ts b/packages/backend/server/src/base/error/def.ts
index 9443c818dc..9e61ac5f2b 100644
--- a/packages/backend/server/src/base/error/def.ts
+++ b/packages/backend/server/src/base/error/def.ts
@@ -590,6 +590,11 @@ export const USER_FRIENDLY_ERRORS = {
     type: 'action_forbidden',
     message: `Action has been taken, no more messages allowed.`,
   },
+  copilot_doc_not_found: {
+    type: 'resource_not_found',
+    args: { docId: 'string' },
+    message: ({ docId }) => `Doc ${docId} not found.`,
+  },
   copilot_message_not_found: {
     type: 'resource_not_found',
     args: { messageId: 'string' },
diff --git a/packages/backend/server/src/base/error/errors.gen.ts b/packages/backend/server/src/base/error/errors.gen.ts
index 6196c06491..e313a1aa6a 100644
--- a/packages/backend/server/src/base/error/errors.gen.ts
+++ b/packages/backend/server/src/base/error/errors.gen.ts
@@ -577,6 +577,16 @@ export class CopilotActionTaken extends UserFriendlyError {
   }
 }
 @ObjectType()
+class CopilotDocNotFoundDataType {
+  @Field() docId!: string
+}
+
+export class CopilotDocNotFound extends UserFriendlyError {
+  constructor(args: CopilotDocNotFoundDataType, message?: string | ((args: CopilotDocNotFoundDataType) => string)) {
+    super('resource_not_found', 'copilot_doc_not_found', message, args);
+  }
+}
+@ObjectType()
 class CopilotMessageNotFoundDataType {
   @Field() messageId!: string
 }
@@ -848,6 +858,7 @@ export enum ErrorNames {
   COPILOT_FAILED_TO_CREATE_MESSAGE,
   UNSPLASH_IS_NOT_CONFIGURED,
   COPILOT_ACTION_TAKEN,
+  COPILOT_DOC_NOT_FOUND,
   COPILOT_MESSAGE_NOT_FOUND,
   COPILOT_PROMPT_NOT_FOUND,
   COPILOT_PROMPT_INVALID,
@@ -880,5 +891,5 @@ registerEnumType(ErrorNames, {
 export const ErrorDataUnionType = createUnionType({
   name: 'ErrorDataUnion',
   types: () =>
-    [QueryTooLongDataType, WrongSignInCredentialsDataType, UnknownOauthProviderDataType, MissingOauthQueryParameterDataType, InvalidEmailDataType, InvalidPasswordLengthDataType, WorkspacePermissionNotFoundDataType, SpaceNotFoundDataType, MemberNotFoundInSpaceDataType, NotInSpaceDataType, AlreadyInSpaceDataType, SpaceAccessDeniedDataType, SpaceOwnerNotFoundDataType, SpaceShouldHaveOnlyOneOwnerDataType, DocNotFoundDataType, DocAccessDeniedDataType, VersionRejectedDataType, InvalidHistoryTimestampDataType, DocHistoryNotFoundDataType, BlobNotFoundDataType, ExpectToGrantDocUserRolesDataType, ExpectToRevokeDocUserRolesDataType, ExpectToUpdateDocUserRoleDataType, UnsupportedSubscriptionPlanDataType, SubscriptionAlreadyExistsDataType, SubscriptionNotExistsDataType, SameSubscriptionRecurringDataType, SubscriptionPlanNotFoundDataType, CopilotMessageNotFoundDataType, CopilotPromptNotFoundDataType, CopilotProviderSideErrorDataType, CopilotInvalidContextDataType, CopilotContextFileNotSupportedDataType, CopilotFailedToModifyContextDataType, CopilotFailedToMatchContextDataType, RuntimeConfigNotFoundDataType, InvalidRuntimeConfigTypeDataType, InvalidLicenseUpdateParamsDataType, WorkspaceMembersExceedLimitToDowngradeDataType] as const,
+    [QueryTooLongDataType, WrongSignInCredentialsDataType, UnknownOauthProviderDataType, MissingOauthQueryParameterDataType, InvalidEmailDataType, InvalidPasswordLengthDataType, WorkspacePermissionNotFoundDataType, SpaceNotFoundDataType, MemberNotFoundInSpaceDataType, NotInSpaceDataType, AlreadyInSpaceDataType, SpaceAccessDeniedDataType, SpaceOwnerNotFoundDataType, SpaceShouldHaveOnlyOneOwnerDataType, DocNotFoundDataType, DocAccessDeniedDataType, VersionRejectedDataType, InvalidHistoryTimestampDataType, DocHistoryNotFoundDataType, BlobNotFoundDataType, ExpectToGrantDocUserRolesDataType, ExpectToRevokeDocUserRolesDataType, ExpectToUpdateDocUserRoleDataType, UnsupportedSubscriptionPlanDataType, SubscriptionAlreadyExistsDataType, SubscriptionNotExistsDataType, SameSubscriptionRecurringDataType, SubscriptionPlanNotFoundDataType, CopilotDocNotFoundDataType, CopilotMessageNotFoundDataType, CopilotPromptNotFoundDataType, CopilotProviderSideErrorDataType, CopilotInvalidContextDataType, CopilotContextFileNotSupportedDataType, CopilotFailedToModifyContextDataType, CopilotFailedToMatchContextDataType, RuntimeConfigNotFoundDataType, InvalidRuntimeConfigTypeDataType, InvalidLicenseUpdateParamsDataType, WorkspaceMembersExceedLimitToDowngradeDataType] as const,
 });
diff --git a/packages/backend/server/src/plugins/copilot/resolver.ts b/packages/backend/server/src/plugins/copilot/resolver.ts
index 1b2a13b040..788da54ffa 100644
--- a/packages/backend/server/src/plugins/copilot/resolver.ts
+++ b/packages/backend/server/src/plugins/copilot/resolver.ts
@@ -21,6 +21,7 @@ import GraphQLUpload from 'graphql-upload/GraphQLUpload.mjs';
 
 import {
   CallMetric,
+  CopilotDocNotFound,
   CopilotFailedToCreateMessage,
   CopilotSessionNotFound,
   type FileUpload,
@@ -381,6 +382,11 @@ export class CopilotResolver {
       return new TooManyRequest('Server is busy');
     }
 
+    if (options.workspaceId === options.docId) {
+      // filter out session create request for root doc
+      throw new CopilotDocNotFound({ docId: options.docId });
+    }
+
     await this.chatSession.checkQuota(user.id);
 
     return await this.chatSession.create({
@@ -443,6 +449,11 @@ export class CopilotResolver {
       return new TooManyRequest('Server is busy');
     }
 
+    if (options.workspaceId === options.docId) {
+      // filter out session create request for root doc
+      throw new CopilotDocNotFound({ docId: options.docId });
+    }
+
     await this.chatSession.checkQuota(user.id);
 
     return await this.chatSession.fork({
diff --git a/packages/backend/server/src/schema.gql b/packages/backend/server/src/schema.gql
index 2d5ef838de..24a5f75421 100644
--- a/packages/backend/server/src/schema.gql
+++ b/packages/backend/server/src/schema.gql
@@ -88,6 +88,10 @@ type CopilotContextListItem {
   status: ContextFileStatus
 }
 
+type CopilotDocNotFoundDataType {
+  docId: String!
+}
+
 type CopilotFailedToMatchContextDataType {
   content: String!
   contextId: String!
@@ -311,7 +315,7 @@ type EditorType {
   name: String!
 }
 
-union ErrorDataUnion = AlreadyInSpaceDataType | BlobNotFoundDataType | CopilotContextFileNotSupportedDataType | CopilotFailedToMatchContextDataType | CopilotFailedToModifyContextDataType | CopilotInvalidContextDataType | CopilotMessageNotFoundDataType | CopilotPromptNotFoundDataType | CopilotProviderSideErrorDataType | DocAccessDeniedDataType | DocHistoryNotFoundDataType | DocNotFoundDataType | ExpectToGrantDocUserRolesDataType | ExpectToRevokeDocUserRolesDataType | ExpectToUpdateDocUserRoleDataType | InvalidEmailDataType | InvalidHistoryTimestampDataType | InvalidLicenseUpdateParamsDataType | InvalidPasswordLengthDataType | InvalidRuntimeConfigTypeDataType | MemberNotFoundInSpaceDataType | MissingOauthQueryParameterDataType | NotInSpaceDataType | QueryTooLongDataType | RuntimeConfigNotFoundDataType | SameSubscriptionRecurringDataType | SpaceAccessDeniedDataType | SpaceNotFoundDataType | SpaceOwnerNotFoundDataType | SpaceShouldHaveOnlyOneOwnerDataType | SubscriptionAlreadyExistsDataType | SubscriptionNotExistsDataType | SubscriptionPlanNotFoundDataType | UnknownOauthProviderDataType | UnsupportedSubscriptionPlanDataType | VersionRejectedDataType | WorkspaceMembersExceedLimitToDowngradeDataType | WorkspacePermissionNotFoundDataType | WrongSignInCredentialsDataType
+union ErrorDataUnion = AlreadyInSpaceDataType | BlobNotFoundDataType | CopilotContextFileNotSupportedDataType | CopilotDocNotFoundDataType | CopilotFailedToMatchContextDataType | CopilotFailedToModifyContextDataType | CopilotInvalidContextDataType | CopilotMessageNotFoundDataType | CopilotPromptNotFoundDataType | CopilotProviderSideErrorDataType | DocAccessDeniedDataType | DocHistoryNotFoundDataType | DocNotFoundDataType | ExpectToGrantDocUserRolesDataType | ExpectToRevokeDocUserRolesDataType | ExpectToUpdateDocUserRoleDataType | InvalidEmailDataType | InvalidHistoryTimestampDataType | InvalidLicenseUpdateParamsDataType | InvalidPasswordLengthDataType | InvalidRuntimeConfigTypeDataType | MemberNotFoundInSpaceDataType | MissingOauthQueryParameterDataType | NotInSpaceDataType | QueryTooLongDataType | RuntimeConfigNotFoundDataType | SameSubscriptionRecurringDataType | SpaceAccessDeniedDataType | SpaceNotFoundDataType | SpaceOwnerNotFoundDataType | SpaceShouldHaveOnlyOneOwnerDataType | SubscriptionAlreadyExistsDataType | SubscriptionNotExistsDataType | SubscriptionPlanNotFoundDataType | UnknownOauthProviderDataType | UnsupportedSubscriptionPlanDataType | VersionRejectedDataType | WorkspaceMembersExceedLimitToDowngradeDataType | WorkspacePermissionNotFoundDataType | WrongSignInCredentialsDataType
 
 enum ErrorNames {
   ACCESS_DENIED
@@ -329,6 +333,7 @@ enum ErrorNames {
   CAPTCHA_VERIFICATION_FAILED
   COPILOT_ACTION_TAKEN
   COPILOT_CONTEXT_FILE_NOT_SUPPORTED
+  COPILOT_DOC_NOT_FOUND
   COPILOT_FAILED_TO_CREATE_MESSAGE
   COPILOT_FAILED_TO_GENERATE_TEXT
   COPILOT_FAILED_TO_MATCH_CONTEXT