diff --git a/app/assets/javascripts/discourse/app/components/d-modal.hbs b/app/assets/javascripts/discourse/app/components/d-modal.hbs
index 5c50992aca8..3d56cb2f19f 100644
--- a/app/assets/javascripts/discourse/app/components/d-modal.hbs
+++ b/app/assets/javascripts/discourse/app/components/d-modal.hbs
@@ -63,6 +63,7 @@
 
           {{yield to="belowHeader"}}
 
+          {{this.validateFlashType @flashType}}
           {{#if @flash}}
             <div
               id="modal-alert"
diff --git a/app/assets/javascripts/discourse/app/components/d-modal.js b/app/assets/javascripts/discourse/app/components/d-modal.js
index 74d273caf70..8afc0436043 100644
--- a/app/assets/javascripts/discourse/app/components/d-modal.js
+++ b/app/assets/javascripts/discourse/app/components/d-modal.js
@@ -8,6 +8,8 @@ export const CLOSE_INITIATED_BY_ESC = "initiatedByESC";
 export const CLOSE_INITIATED_BY_CLICK_OUTSIDE = "initiatedByClickOut";
 export const CLOSE_INITIATED_BY_MODAL_SHOW = "initiatedByModalShow";
 
+const FLASH_TYPES = ["success", "error", "warning", "info"];
+
 export default class DModal extends Component {
   @service modal;
   @tracked wrapperElement;
@@ -161,4 +163,11 @@ export default class DModal extends Component {
   handleCloseButton() {
     this.args.closeModal({ initiatedBy: CLOSE_INITIATED_BY_BUTTON });
   }
+
+  @action
+  validateFlashType(type) {
+    if (type && !FLASH_TYPES.includes(type)) {
+      throw `@flashType must be one of ${FLASH_TYPES.join(", ")}`;
+    }
+  }
 }