diff --git a/src/orderBy.ts b/src/orderBy.ts
index 547c978..1dc9bc0 100644
--- a/src/orderBy.ts
+++ b/src/orderBy.ts
@@ -6,5 +6,8 @@ export default function orderBy<TSource, TKey>(this: Iterable<TSource>, keySelec
     if (keySelector == null) {
         keySelector = value => value as any;
     }
+    if (this instanceof OrderedEnumerable) {
+        return (this as any).thenBy(keySelector);
+    }
     return new OrderedEnumerable(this, keySelector, false);
 }
diff --git a/src/orderByDescending.ts b/src/orderByDescending.ts
index e5813e6..505d8f4 100644
--- a/src/orderByDescending.ts
+++ b/src/orderByDescending.ts
@@ -6,5 +6,8 @@ export default function orderByDescending<TSource, TKey>(this: Iterable<TSource>
     if (keySelector == null) {
         keySelector = value => value as any;
     }
+    if (this instanceof OrderedEnumerable) {
+        return (this as any).thenByDescending(keySelector);
+    }
     return new OrderedEnumerable(this, keySelector, true);
 }