diff --git a/umap/static/umap/js/modules/rules.js b/umap/static/umap/js/modules/rules.js
index fa802efb..dbeb88e0 100644
--- a/umap/static/umap/js/modules/rules.js
+++ b/umap/static/umap/js/modules/rules.js
@@ -74,7 +74,8 @@ class Rule {
     if (vars.length !== 2) return
     this.key = vars[0]
     this.expected = vars[1]
-    if (!Number.isNaN(this.expected)) this.cast = Number.parseFloat
+    // biome-ignore lint/suspicious/noGlobalIsNan: expected might not be a number.
+    if (!isNaN(this.expected)) this.cast = Number.parseFloat
     else if (['true', 'false'].includes(this.expected)) this.cast = (v) => !!v
     this.expected = this.cast(this.expected)
   }
diff --git a/umap/static/umap/test/DataLayer.js b/umap/static/umap/test/DataLayer.js
index 201f8a7f..26ba7d61 100644
--- a/umap/static/umap/test/DataLayer.js
+++ b/umap/static/umap/test/DataLayer.js
@@ -316,7 +316,7 @@ describe('U.DataLayer', () => {
       let icon = qs('div.umap-div-icon .icon_container')
       poly.properties.mycolor = 'DarkGoldenRod'
       marker.properties.mycolor = 'DarkRed'
-      delete marker.properties._umap_options.color
+      marker.properties._umap_options.color = undefined
       assert.notOk(qs('path[fill="DarkGoldenRod"]'))
       assert.equal(icon.style.backgroundColor, 'olivedrab')
       datalayer.options.color = '{mycolor}'