diff --git a/src/System.Collections.Immutable/src/System/Collections/Immutable/ImmutableArray_1.Builder.cs b/src/System.Collections.Immutable/src/System/Collections/Immutable/ImmutableArray_1.Builder.cs
index 482215723c4f..a5ba7b2e9863 100644
--- a/src/System.Collections.Immutable/src/System/Collections/Immutable/ImmutableArray_1.Builder.cs
+++ b/src/System.Collections.Immutable/src/System/Collections/Immutable/ImmutableArray_1.Builder.cs
@@ -5,6 +5,7 @@
 using System.Collections.Generic;
 using System.Diagnostics;
 using System.Diagnostics.Contracts;
+using System.Runtime.CompilerServices;
 
 namespace System.Collections.Immutable
 {
@@ -247,7 +248,28 @@ public void Insert(int index, T item)
             /// Adds an item to the <see cref="ICollection{T}"/>.
             /// </summary>
             /// <param name="item">The object to add to the <see cref="ICollection{T}"/>.</param>
+            [MethodImpl(MethodImplOptions.AggressiveInlining)]
             public void Add(T item)
+            {
+                int count = _count;
+                T[] elements = _elements;
+
+                // PERF: The uint-casts allow the JIT to eliminate bound-checks.
+                // https://github.com/dotnet/coreclr/pull/9773
+                if ((uint)count < (uint)elements.Length)
+                {
+                    elements[count] = item;
+                    _count = count + 1;
+                }
+                else
+                {
+                    AddWithResize(item);
+                }
+            }
+
+            // Specify NoInlining so that we are guaranteed an opportunity to service this method
+            [MethodImpl(MethodImplOptions.NoInlining)]
+            private void AddWithResize(T item)
             {
                 int newCount = _count + 1;
                 this.EnsureCapacity(newCount);