diff --git a/types/chartist/chartist-tests.ts b/types/chartist/chartist-tests.ts
index 270e6e0970..bd7006723e 100644
--- a/types/chartist/chartist-tests.ts
+++ b/types/chartist/chartist-tests.ts
@@ -343,6 +343,7 @@ chart2.on('draw', (data: any) => {
             style: 'fill-opacity: 1'
         }, 'ct-area');
 
+        triangle.attr({ style: 'fill-opacity: .5' });
         // With data.element we get the Chartist SVG wrapper and we can replace the original point drawn by Chartist with our newly created triangle
         data.element.replace(triangle);
     }
diff --git a/types/chartist/index.d.ts b/types/chartist/index.d.ts
index 80cc589ee2..3d72210c73 100644
--- a/types/chartist/index.d.ts
+++ b/types/chartist/index.d.ts
@@ -534,7 +534,7 @@ declare namespace Chartist {
         /**
          * Set attributes on the current SVG element of the wrapper you're currently working on.
          */
-        attr(attributes: Object | string, ns: string): Object | string;
+        attr(attributes: Object | string, ns?: string): Object | string;
 
         /**
          * Create a new SVG element whose wrapper object will be selected for further operations. This way you can also create nested groups easily.