diff --git a/src/libraries/System.Linq/ref/System.Linq.cs b/src/libraries/System.Linq/ref/System.Linq.cs
index 215ec4b4d34e8..a35e99ba3c232 100644
--- a/src/libraries/System.Linq/ref/System.Linq.cs
+++ b/src/libraries/System.Linq/ref/System.Linq.cs
@@ -148,9 +148,9 @@ public static System.Collections.Generic.IEnumerable<
         public static System.Linq.IOrderedEnumerable<TSource> OrderBy<TSource, TKey>(this System.Collections.Generic.IEnumerable<TSource> source, System.Func<TSource, TKey> keySelector) { throw null; }
         public static System.Linq.IOrderedEnumerable<TSource> OrderBy<TSource, TKey>(this System.Collections.Generic.IEnumerable<TSource> source, System.Func<TSource, TKey> keySelector, System.Collections.Generic.IComparer<TKey>? comparer) { throw null; }
         public static System.Linq.IOrderedEnumerable<T> OrderDescending<T>(this System.Collections.Generic.IEnumerable<T> source) { throw null; }
-        public static System.Linq.IOrderedEnumerable<T> OrderDescending<T>(this System.Collections.Generic.IEnumerable<T> source, System.Collections.Generic.IComparer<T> comparer) { throw null; }
+        public static System.Linq.IOrderedEnumerable<T> OrderDescending<T>(this System.Collections.Generic.IEnumerable<T> source, System.Collections.Generic.IComparer<T>? comparer) { throw null; }
         public static System.Linq.IOrderedEnumerable<T> Order<T>(this System.Collections.Generic.IEnumerable<T> source) { throw null; }
-        public static System.Linq.IOrderedEnumerable<T> Order<T>(this System.Collections.Generic.IEnumerable<T> source, System.Collections.Generic.IComparer<T> comparer) { throw null; }
+        public static System.Linq.IOrderedEnumerable<T> Order<T>(this System.Collections.Generic.IEnumerable<T> source, System.Collections.Generic.IComparer<T>? comparer) { throw null; }
         public static System.Collections.Generic.IEnumerable<TSource> Prepend<TSource>(this System.Collections.Generic.IEnumerable<TSource> source, TSource element) { throw null; }
         public static System.Collections.Generic.IEnumerable<int> Range(int start, int count) { throw null; }
         public static System.Collections.Generic.IEnumerable<TResult> Repeat<TResult>(TResult element, int count) { throw null; }
diff --git a/src/libraries/System.Linq/src/System/Linq/OrderBy.cs b/src/libraries/System.Linq/src/System/Linq/OrderBy.cs
index c0bddf796f2b0..8d4734225b1a9 100644
--- a/src/libraries/System.Linq/src/System/Linq/OrderBy.cs
+++ b/src/libraries/System.Linq/src/System/Linq/OrderBy.cs
@@ -41,7 +41,7 @@ public static IOrderedEnumerable<T> Order<T>(this IEnumerable<T> source) =>
         ///
         /// If comparer is <see langword="null"/>, the default comparer <see cref="Comparer{T}.Default"/> is used to compare elements.
         /// </remarks>
-        public static IOrderedEnumerable<T> Order<T>(this IEnumerable<T> source, IComparer<T> comparer) =>
+        public static IOrderedEnumerable<T> Order<T>(this IEnumerable<T> source, IComparer<T>? comparer) =>
             OrderBy(source, static element => element, comparer);
 
         public static IOrderedEnumerable<TSource> OrderBy<TSource, TKey>(this IEnumerable<TSource> source, Func<TSource, TKey> keySelector)
@@ -84,7 +84,7 @@ public static IOrderedEnumerable<T> OrderDescending<T>(this IEnumerable<T> sourc
         ///
         /// If comparer is <see langword="null"/>, the default comparer <see cref="Comparer{T}.Default"/> is used to compare elements.
         /// </remarks>
-        public static IOrderedEnumerable<T> OrderDescending<T>(this IEnumerable<T> source, IComparer<T> comparer) =>
+        public static IOrderedEnumerable<T> OrderDescending<T>(this IEnumerable<T> source, IComparer<T>? comparer) =>
             OrderByDescending(source, static element => element, comparer);
 
         public static IOrderedEnumerable<TSource> OrderByDescending<TSource, TKey>(this IEnumerable<TSource> source, Func<TSource, TKey> keySelector) =>