diff --git a/umap/static/umap/js/modules/caption.js b/umap/static/umap/js/modules/caption.js
index 21768dde..1ec7c218 100644
--- a/umap/static/umap/js/modules/caption.js
+++ b/umap/static/umap/js/modules/caption.js
@@ -74,10 +74,10 @@ export default class Caption extends Utils.WithTemplate {
     this.addCredits()
     if (this._umap.properties.created_at) {
       const created_at = translate('created at {date}', {
-        date: new Date(this._umap.properties.created_at).toLocaleDateString(),
+        date: this._umap.createdAt.toLocaleDateString(),
       })
       const modified_at = translate('modified at {date}', {
-        date: new Date(this._umap.properties.modified_at).toLocaleDateString(),
+        date: this._umap.modifiedAt.toLocaleDateString(),
       })
       this.elements.dates.innerHTML = `${created_at} - ${modified_at}`
     } else {
diff --git a/umap/static/umap/js/modules/data/layer.js b/umap/static/umap/js/modules/data/layer.js
index f05b2ce3..7dc03e8f 100644
--- a/umap/static/umap/js/modules/data/layer.js
+++ b/umap/static/umap/js/modules/data/layer.js
@@ -220,6 +220,7 @@ export class DataLayer {
     this._loading = true
     const [geojson, response, error] = await this._umap.server.get(this._dataUrl())
     if (!error) {
+      this._umap.modifiedAt = response.headers.get('last-modified')
       this.setReferenceVersion({ response, sync: false })
       // FIXME: for now the _umap_options property is set dynamically from backend
       // And thus it's not in the geojson file in the server
@@ -303,7 +304,10 @@ export class DataLayer {
   async getUrl(url, initialUrl) {
     const response = await this._umap.request.get(url)
     return new Promise((resolve) => {
-      if (response?.ok) return resolve(response.text())
+      if (response?.ok) {
+        this._umap.modifiedAt = response.headers.get('last-modified')
+        return resolve(response.text())
+      }
       Alert.error(
         translate('Cannot load remote data for layer "{layer}" with url "{url}"', {
           layer: this.getName(),
diff --git a/umap/static/umap/js/modules/umap.js b/umap/static/umap/js/modules/umap.js
index 51c98552..bcff5c50 100644
--- a/umap/static/umap/js/modules/umap.js
+++ b/umap/static/umap/js/modules/umap.js
@@ -57,6 +57,8 @@ export default class Umap {
       },
       geojson.properties
     )
+    this.createdAt = new Date(this.properties.created_at)
+    this.modifiedAt = this.properties.modified_at
     this.searchParams = new URLSearchParams(window.location.search)
 
     // Locale name (pt_PT, en_US…)
@@ -237,6 +239,21 @@ export default class Umap {
     this._activeFeature = feature
   }
 
+  get modifiedAt() {
+    return this._modifiedAt
+  }
+
+  set modifiedAt(at) {
+    if (!at) return
+    if (typeof at === 'string') {
+      at = new Date(at)
+    }
+    if (!this._modifiedAt || at > this._modifiedAt) {
+      console.log('set modifiedAt to', at)
+      this._modifiedAt = at
+    }
+  }
+
   setPropertiesFromQueryString() {
     const asBoolean = (key) => {
       const value = this.searchParams.get(key)