diff --git a/conf/config.default.xml b/conf/config.default.xml
index e7a4fcbc7b..991d845c8c 100644
--- a/conf/config.default.xml
+++ b/conf/config.default.xml
@@ -40,6 +40,7 @@
         <no_anonymous_access>0</no_anonymous_access>
         <jwt_secret>my_secret</jwt_secret>
         <enabled_websockets>0</enabled_websockets>
+        <preflight_query_timeout_ms>3000</preflight_query_timeout_ms>
     </global>
     <calc_backend>
         <type>rq</type>
diff --git a/conf/config.rng b/conf/config.rng
index 5ef4f61556..d9be38fcbd 100644
--- a/conf/config.rng
+++ b/conf/config.rng
@@ -415,6 +415,16 @@
                             </oneOrMore>
                         </element>
                     </optional>
+                    <optional>
+                        <element name="preflight_query_timeout_ms">
+                            <a:documentation>
+                                For preflight queries, this speicifies how long KonText client-side waits
+                                for the query. In case it is not finished in the limit, the client will
+                                consider the query a &quot;long one&quot; and warn user accordingly.
+                            </a:documentation>
+                            <data type="nonNegativeInteger" />
+                        </element>
+                    </optional>
                 </interleave>
             </element>
             <element name="calc_backend">
diff --git a/lib/action/model/base.py b/lib/action/model/base.py
index 0518a55491..31440a7fed 100644
--- a/lib/action/model/base.py
+++ b/lib/action/model/base.py
@@ -126,6 +126,7 @@ async def add_globals(self, app: Sanic, action_props: ActionProps, result: Dict[
         result['issue_reporting_action'] = None
         result['help_links'] = {}
         result['_version'] = None
+        result['preflight_query_timeout_ms'] = settings.get_int('global', 'preflight_query_timeout_ms', 0)
         return result
 
     def init_menu(self, result):
diff --git a/lib/action/model/corpus.py b/lib/action/model/corpus.py
index 72e444d605..fd3ba9fff3 100644
--- a/lib/action/model/corpus.py
+++ b/lib/action/model/corpus.py
@@ -19,7 +19,6 @@
 
 
 import logging
-import urllib.parse
 from dataclasses import asdict
 from functools import partial
 from typing import (
diff --git a/public/files/js/app/navigation/index.ts b/public/files/js/app/navigation/index.ts
index 19cbb9bf07..4c6d6c9c1c 100644
--- a/public/files/js/app/navigation/index.ts
+++ b/public/files/js/app/navigation/index.ts
@@ -68,12 +68,13 @@ export function parseUrlArgs(args:string):Array<[string, string]> {
  *
  */
 interface AjaxRequestProps {
-    accept:string,
-    contentType:string,
-    responseType:XMLHttpRequestResponseType,
-    method:string,
-    requestBody:string,
-    url:string
+    accept:string;
+    contentType:string;
+    responseType:XMLHttpRequestResponseType;
+    method:string;
+    requestBody:string;
+    url:string;
+    timeout:number;
 }
 
 /**
@@ -253,7 +254,8 @@ export class AppNavigation implements Kontext.IURLHandler, Kontext.IAjaxHandler
             responseType: options.responseType,
             method,
             requestBody: body,
-            url
+            url,
+            timeout: options.timeout ? options.timeout : 0
         }
     }
 
@@ -282,7 +284,9 @@ export class AppNavigation implements Kontext.IURLHandler, Kontext.IAjaxHandler
             responseType: callArgs.responseType,
             headers: {
                 'Content-Type': callArgs.contentType
-            }
+            },
+            timeout: callArgs.timeout
+
         }).pipe(
             map<RxAjaxResponse<T>, T>(v => v.response)
         );
diff --git a/public/files/js/models/query/first.ts b/public/files/js/models/query/first.ts
index 0426c3422e..a66ae457aa 100644
--- a/public/files/js/models/query/first.ts
+++ b/public/files/js/models/query/first.ts
@@ -22,7 +22,8 @@
 
 import { IFullActionControl } from 'kombo';
 import { Observable, of as rxOf } from 'rxjs';
-import { tap, map, concatMap, reduce } from 'rxjs/operators';
+import { AjaxTimeoutError } from 'rxjs/ajax';
+import { tap, map, concatMap, reduce, catchError } from 'rxjs/operators';
 import { Dict, tuple, List, pipe, HTTP, Rx } from 'cnc-tskit';
 
 import * as Kontext from '../../types/kontext';
@@ -1119,9 +1120,20 @@ export class FirstQueryFormModel extends QueryFormModel<FirstQueryFormModelState
             ),
             this.createPreflightArgs(contextData, ttSelections, preflightSubc),
             {
-                contentType: 'application/json'
+                contentType: 'application/json',
+                timeout: this.pageModel.getConf('PreflightTimeoutMs') || 0
             }
         ).pipe(
+            catchError(
+                err => {
+                    if (err instanceof AjaxTimeoutError) {
+                        return rxOf({
+                            sizeIpm: preflightSubc.threshold_ipm + 1
+                        });
+                    }
+                    throw err;
+                }
+            ),
             map(
                 ans => ({
                     contextData,
diff --git a/public/files/js/types/kontext.ts b/public/files/js/types/kontext.ts
index 50cfdd6598..2a9db8dfa9 100644
--- a/public/files/js/types/kontext.ts
+++ b/public/files/js/types/kontext.ts
@@ -356,6 +356,7 @@ export interface AjaxOptions {
     contentType?:string;
     responseType?:XMLHttpRequestResponseType;
     accept?:string;
+    timeout?:number;
 }
 
 export type AsyncTaskStatus = 'PENDING'|'STARTED'|'SUCCESS'|'FAILURE';
diff --git a/templates/document.html b/templates/document.html
index f564e68180..5fd1be8de9 100644
--- a/templates/document.html
+++ b/templates/document.html
@@ -49,5 +49,6 @@
 __conf.TextDirectionRTL = {{ righttoleft|default(false, true)|to_json }};
 __conf.InitialFreqLevel = {{ last_freq_level|default(1, true)|to_json }};
 __conf.maxDispersionResolution = {{ max_dispersion_resulution|default(0, true)|to_json }};
+__conf.PreflightTimeoutMs = {{ preflight_query_timeout_ms|to_json }};
 __conf.manateeIsCustomCNC = {{ manatee_is_custom_cnc|to_json }};
 {% endblock %}
\ No newline at end of file