diff --git a/apps/common/main/lib/component/InputField.js b/apps/common/main/lib/component/InputField.js
index 069079566..75fe653ac 100644
--- a/apps/common/main/lib/component/InputField.js
+++ b/apps/common/main/lib/component/InputField.js
@@ -358,10 +358,10 @@ define([
                 return true;
             },
 
-            showError: function(errors) {
+            showError: function(errors, isWarning) {
                 var me = this;
                 if (!_.isEmpty(errors)) {
-                    me.cmpEl.addClass('error');
+                    me.cmpEl.addClass(isWarning ? 'warning' : 'error');
 
                     var errorBadge = me.cmpEl.find('.input-error'),
                         modalParents = errorBadge.closest('.asc-window'),
@@ -380,7 +380,12 @@ define([
                     }
                 } else {
                     me.cmpEl.removeClass('error');
+                    me.cmpEl.removeClass('warning');
                 }
+            },
+
+            showWarning: function(errors) {
+                this.showError(errors, true);
             }
         }
     })());
diff --git a/apps/common/main/resources/img/controls/common-controls.png b/apps/common/main/resources/img/controls/common-controls.png
index 8694bd120..03fb0999d 100755
Binary files a/apps/common/main/resources/img/controls/common-controls.png and b/apps/common/main/resources/img/controls/common-controls.png differ
diff --git a/apps/common/main/resources/img/controls/common-controls@1.5x.png b/apps/common/main/resources/img/controls/common-controls@1.5x.png
index 1d29d593f..1fd7da019 100644
Binary files a/apps/common/main/resources/img/controls/common-controls@1.5x.png and b/apps/common/main/resources/img/controls/common-controls@1.5x.png differ
diff --git a/apps/common/main/resources/img/controls/common-controls@2x.png b/apps/common/main/resources/img/controls/common-controls@2x.png
index 1c1de5bcb..7d368d53e 100755
Binary files a/apps/common/main/resources/img/controls/common-controls@2x.png and b/apps/common/main/resources/img/controls/common-controls@2x.png differ
diff --git a/apps/common/main/resources/less/asc-mixins.less b/apps/common/main/resources/less/asc-mixins.less
index c7e8a6d22..5f3f0311e 100644
--- a/apps/common/main/resources/less/asc-mixins.less
+++ b/apps/common/main/resources/less/asc-mixins.less
@@ -200,7 +200,7 @@
 
 @common-controls-width: 100px;
 .img-commonctrl, 
-        .dropdown-menu li .checked:before, .input-error:before,
+        .dropdown-menu li .checked:before, .input-error:before, .input-warning:before,
         .btn-toolbar .icon.img-commonctrl, .list-item div.checked:before
 {
     background-image: if(@icon-src-base64, data-uri(%("%s",'@{common-image-path}/@{common-controls}')), ~"url(@{common-image-const-path}/@{common-controls})");
diff --git a/apps/common/main/resources/less/input.less b/apps/common/main/resources/less/input.less
index ae0c3328a..4fcbd8755 100644
--- a/apps/common/main/resources/less/input.less
+++ b/apps/common/main/resources/less/input.less
@@ -61,6 +61,18 @@
             display: block;
         }
     }
+
+    &.warning {
+        input:not([disabled]) + .input-error {
+            display: block;
+        }
+
+        .input-error {
+            &:before {
+                background-position: @input-warning-offset-x @input-warning-offset-y;
+            }
+        }
+    }
 }
 
 input:required:focus:invalid,
diff --git a/apps/common/main/resources/less/variables.less b/apps/common/main/resources/less/variables.less
index 044f6cbc4..04878d790 100644
--- a/apps/common/main/resources/less/variables.less
+++ b/apps/common/main/resources/less/variables.less
@@ -771,6 +771,10 @@
 @input-error-offset-x: -73px;
 @input-error-offset-y: -170px;
 
+// Input warning
+@input-warning-offset-x: -57px;
+@input-warning-offset-y: -170px;
+
 // Spinner
 @spinner-offset-x: -41px;
 @spinner-offset-y: -187px;
diff --git a/apps/spreadsheeteditor/main/app/view/FormatSettingsDialog.js b/apps/spreadsheeteditor/main/app/view/FormatSettingsDialog.js
index 169b2bb0c..bd3b54791 100644
--- a/apps/spreadsheeteditor/main/app/view/FormatSettingsDialog.js
+++ b/apps/spreadsheeteditor/main/app/view/FormatSettingsDialog.js
@@ -247,6 +247,10 @@ define([
                 me.codesList.deselectAll();
                 me.Format = me.api.asc_convertNumFormatLocal2NumFormat(value);
                 me.lblExample.text(me.api.asc_getLocaleExample(me.Format));
+                if (!me._state.warning) {
+                    input.showWarning([me.txtCustomWarning]);
+                    me._state.warning = true;
+                }
             });
 
             this._decimalPanel      = this.$window.find('.format-decimal');
@@ -423,6 +427,8 @@ define([
             this.Format = record.get('format');
             this.lblExample.text(this.api.asc_getLocaleExample(this.Format));
             this.inputCustomFormat.setValue(record.get('value'));
+            this.inputCustomFormat.showWarning();
+            this._state.warning = false;
         },
 
         onFormatSelect: function(combo, record, e, initFormatInfo) {
@@ -565,7 +571,8 @@ define([
         txtAs10:  'As tenths (5/10)',
         txtAs100: 'As hundredths (50/100)',
         txtSample: 'Sample:',
-        txtNone: 'None'
+        txtNone: 'None',
+        txtCustomWarning: 'Custom format not validated'
 
     }, SSE.Views.FormatSettingsDialog || {}))
 });
\ No newline at end of file
diff --git a/apps/spreadsheeteditor/main/locale/en.json b/apps/spreadsheeteditor/main/locale/en.json
index af2f76408..7a224ebd0 100644
--- a/apps/spreadsheeteditor/main/locale/en.json
+++ b/apps/spreadsheeteditor/main/locale/en.json
@@ -1923,6 +1923,7 @@
   "SSE.Views.FormatSettingsDialog.txtUpto1": "Up to one digit (1/3)",
   "SSE.Views.FormatSettingsDialog.txtUpto2": "Up to two digits (12/25)",
   "SSE.Views.FormatSettingsDialog.txtUpto3": "Up to three digits (131/135)",
+  "SSE.Views.FormatSettingsDialog.txtCustomWarning": "Custom format not validated",
   "SSE.Views.FormulaDialog.sDescription": "Description",
   "SSE.Views.FormulaDialog.textGroupDescription": "Select Function Group",
   "SSE.Views.FormulaDialog.textListDescription": "Select Function",