diff --git a/test/types/expressions.test.ts b/test/types/expressions.test.ts
index 00509363c07..be57ddaf38e 100644
--- a/test/types/expressions.test.ts
+++ b/test/types/expressions.test.ts
@@ -203,3 +203,17 @@ const switchExpr: Expression.Switch = {
     default: 'Hello'
   }
 };
+
+(function gh12058() {
+  const concat: Expression.ConcatArrays = {
+    $concatArrays: [
+      {
+        $cond: {
+          if: { $eq: ['foo', true] },
+          then: [1],
+          else: [2]
+        }
+      }
+    ]
+  };
+})();
diff --git a/types/expressions.d.ts b/types/expressions.d.ts
index 8624b155b6c..69b882b2eb6 100644
--- a/types/expressions.d.ts
+++ b/types/expressions.d.ts
@@ -1104,7 +1104,7 @@ declare module 'mongoose' {
        * @version 3.2
        * @see https://docs.mongodb.com/manual/reference/operator/aggregation/concatArrays/#mongodb-expression-exp.-concatArrays
        */
-      $concatArrays: ArrayExpression[];
+      $concatArrays: Expression[];
     }
 
     export interface Filter {