diff --git a/src/card.ts b/src/card.ts
index f970088f..8a887bbc 100644
--- a/src/card.ts
+++ b/src/card.ts
@@ -377,7 +377,7 @@ export class FrigateCard extends LitElement {
    * @param error The ZodError object from parsing.
    * @returns An array of string error paths.
    */
-  protected _getParseErrorPaths<T>(error: z.ZodError<T>): string[] {
+  protected _getParseErrorPaths<T>(error: z.ZodError<T>): Set<string> | null {
     /* Zod errors involving unions are complex, as Zod may not be able to tell
      * where the 'real' error is vs simply a union option not matching. This
      * function finds all ZodError "issues" that don't have an error with 'type'
@@ -388,7 +388,7 @@ export class FrigateCard extends LitElement {
      * exactly why (or rather Zod simply says it doesn't match any of the
      * available unions). This usually suggests the user specified an incorrect
      * type name entirely. */
-    let contenders: string[] = [];
+    const contenders = new Set<string>();
     if (error && error.issues) {
       for (let i = 0; i < error.issues.length; i++) {
         const issue = error.issues[i];
@@ -396,17 +396,17 @@ export class FrigateCard extends LitElement {
           const unionErrors = (issue as z.ZodInvalidUnionIssue).unionErrors;
           for (let j = 0; j < unionErrors.length; j++) {
             const nestedErrors = this._getParseErrorPaths(unionErrors[j]);
-            if (nestedErrors.length) {
-              contenders = contenders.concat(nestedErrors);
+            if (nestedErrors && nestedErrors.size) {
+              nestedErrors.forEach(contenders.add, contenders);
             }
           }
         } else if (issue.code == 'invalid_type') {
           if (issue.path[issue.path.length - 1] == 'type') {
-            return [];
+            return null;
           }
-          contenders.push(this._getParseErrorPathString(issue.path));
+          contenders.add(this._getParseErrorPathString(issue.path));
         } else if (issue.code != 'custom') {
-          contenders.push(this._getParseErrorPathString(issue.path));
+          contenders.add(this._getParseErrorPathString(issue.path));
         }
       }
     }
@@ -454,8 +454,8 @@ export class FrigateCard extends LitElement {
       throw new Error(
         upgradeMessage +
           `${localize('error.invalid_configuration')}: ` +
-          (hint.length
-            ? JSON.stringify(hint, null, ' ')
+          (hint && hint.size
+            ? JSON.stringify([...hint], null, ' ')
             : localize('error.invalid_configuration_no_hint')),
       );
     }
diff --git a/src/types.ts b/src/types.ts
index 0e37f670..a7c52b24 100644
--- a/src/types.ts
+++ b/src/types.ts
@@ -103,6 +103,8 @@ const customActionSchema = z.object({
   action: z.literal('fire-dom-event'),
 })
 export const frigateCardCustomActionSchema = customActionSchema.merge(z.object({
+  // Syntactic sugar to avoid 'fire-dom-event' as part of an external API.
+  action: z.literal('fire-dom-event').or(z.literal('custom:frigate-card-action').transform(() => 'fire-dom-event')),
   frigate_card_action: z.string(),
 }))
 export type FrigateCardCustomAction = z.infer<typeof frigateCardCustomActionSchema>;