diff --git a/src/app/carbon-estimator-form/carbon-estimator-form.component.html b/src/app/carbon-estimator-form/carbon-estimator-form.component.html
index ba42db63..fbc35036 100644
--- a/src/app/carbon-estimator-form/carbon-estimator-form.component.html
+++ b/src/app/carbon-estimator-form/carbon-estimator-form.component.html
@@ -236,7 +236,7 @@
   <div class="tce-flex tce-gap-4 tce-flex-row-reverse">
     <button
       class="tce-button-calculate tce-px-3 tce-py-2"
-      [ngClass]="!estimatorForm.valid ? 'tce-opacity-50 tce-cursor-not-allowed' : ''"
+      [ngClass]="{ 'tce-opacity-50 tce-cursor-not-allowed': !estimatorForm.valid }"
       type="submit"
       [attr.aria-disabled]="!estimatorForm.valid">
       Calculate