diff --git a/src/libraries/System.Collections.Immutable/src/System/Collections/Immutable/ImmutableList_1.Node.cs b/src/libraries/System.Collections.Immutable/src/System/Collections/Immutable/ImmutableList_1.Node.cs
index de18332bd01788..d89f04ef667460 100644
--- a/src/libraries/System.Collections.Immutable/src/System/Collections/Immutable/ImmutableList_1.Node.cs
+++ b/src/libraries/System.Collections.Immutable/src/System/Collections/Immutable/ImmutableList_1.Node.cs
@@ -808,7 +808,7 @@ internal int LastIndexOf(T item, int index, int count, IEqualityComparer<T>? equ
 
                 Requires.Range(index >= 0 && index < this.Count, nameof(index));
                 Requires.Range(count >= 0 && count <= this.Count, nameof(count));
-                Requires.Argument(index - count + 1 >= 0);
+                Requires.Range(index - count + 1 >= 0, nameof(count));
 
                 equalityComparer ??= EqualityComparer<T>.Default;
                 using (var enumerator = new Enumerator(this, startIndex: index, count: count, reversed: true))
diff --git a/src/libraries/System.Collections.Immutable/tests/ImmutableArrayBuilderTest.cs b/src/libraries/System.Collections.Immutable/tests/ImmutableArrayBuilderTest.cs
index 841bfc451e332d..56d8ebadf4cbd3 100644
--- a/src/libraries/System.Collections.Immutable/tests/ImmutableArrayBuilderTest.cs
+++ b/src/libraries/System.Collections.Immutable/tests/ImmutableArrayBuilderTest.cs
@@ -277,7 +277,9 @@ public void LastIndexOf()
                 (b, v, eq) => b.LastIndexOf(v, b.Count > 0 ? b.Count - 1 : 0, b.Count, eq),
                 (b, v, i) => b.LastIndexOf(v, i),
                 (b, v, i, c) => b.LastIndexOf(v, i, c),
-                (b, v, i, c, eq) => b.LastIndexOf(v, i, c, eq));
+                (b, v, i, c, eq) => b.LastIndexOf(v, i, c, eq),
+                "startIndex",
+                "count");
         }
 
         [Fact]
diff --git a/src/libraries/System.Collections.Immutable/tests/ImmutableArrayTest.cs b/src/libraries/System.Collections.Immutable/tests/ImmutableArrayTest.cs
index f42957f3fac3a1..5dfe21f43cb783 100644
--- a/src/libraries/System.Collections.Immutable/tests/ImmutableArrayTest.cs
+++ b/src/libraries/System.Collections.Immutable/tests/ImmutableArrayTest.cs
@@ -802,7 +802,9 @@ public void LastIndexOf()
                 (b, v, eq) => b.LastIndexOf(v, eq),
                 (b, v, i) => b.LastIndexOf(v, i),
                 (b, v, i, c) => b.LastIndexOf(v, i, c),
-                (b, v, i, c, eq) => b.LastIndexOf(v, i, c, eq));
+                (b, v, i, c, eq) => b.LastIndexOf(v, i, c, eq),
+                "startIndex",
+                "count");
         }
 
         [Theory]
diff --git a/src/libraries/System.Collections.Immutable/tests/ImmutableListBuilderTest.cs b/src/libraries/System.Collections.Immutable/tests/ImmutableListBuilderTest.cs
index 741dfbd085cde4..bdb308977c69d1 100644
--- a/src/libraries/System.Collections.Immutable/tests/ImmutableListBuilderTest.cs
+++ b/src/libraries/System.Collections.Immutable/tests/ImmutableListBuilderTest.cs
@@ -345,7 +345,9 @@ public void LastIndexOf()
                 (b, v, eq) => b.LastIndexOf(v, b.Count > 0 ? b.Count - 1 : 0, b.Count, eq),
                 (b, v, i) => b.LastIndexOf(v, i),
                 (b, v, i, c) => b.LastIndexOf(v, i, c),
-                (b, v, i, c, eq) => b.LastIndexOf(v, i, c, eq));
+                (b, v, i, c, eq) => b.LastIndexOf(v, i, c, eq),
+                "index",
+                "count");
         }
 
         [Fact]
diff --git a/src/libraries/System.Collections.Immutable/tests/ImmutableListTest.cs b/src/libraries/System.Collections.Immutable/tests/ImmutableListTest.cs
index 429c6a01e19241..6137f1b968a7b4 100644
--- a/src/libraries/System.Collections.Immutable/tests/ImmutableListTest.cs
+++ b/src/libraries/System.Collections.Immutable/tests/ImmutableListTest.cs
@@ -512,14 +512,18 @@ public void LastIndexOf()
                 (b, v, eq) => b.LastIndexOf(v, eq),
                 (b, v, i) => b.LastIndexOf(v, i),
                 (b, v, i, c) => b.LastIndexOf(v, i, c),
-                (b, v, i, c, eq) => b.LastIndexOf(v, i, c, eq));
+                (b, v, i, c, eq) => b.LastIndexOf(v, i, c, eq),
+                "index",
+                "count");
             IndexOfTests.LastIndexOfTest(
                 seq => (IImmutableList<int>)ImmutableList.CreateRange(seq),
                 (b, v) => b.LastIndexOf(v),
                 (b, v, eq) => b.LastIndexOf(v, eq),
                 (b, v, i) => b.LastIndexOf(v, i),
                 (b, v, i, c) => b.LastIndexOf(v, i, c),
-                (b, v, i, c, eq) => b.LastIndexOf(v, i, c, eq));
+                (b, v, i, c, eq) => b.LastIndexOf(v, i, c, eq),
+                "index",
+                "count");
         }
 
         [Fact]
diff --git a/src/libraries/System.Collections.Immutable/tests/ImmutableListTestBase.cs b/src/libraries/System.Collections.Immutable/tests/ImmutableListTestBase.cs
index e7237c9de74562..135ccf95ab23b9 100644
--- a/src/libraries/System.Collections.Immutable/tests/ImmutableListTestBase.cs
+++ b/src/libraries/System.Collections.Immutable/tests/ImmutableListTestBase.cs
@@ -177,14 +177,17 @@ public void FindLastIndexTest()
             ImmutableList<int> singleElementList = ImmutableList.Create(10);
             Assert.Equal(0, this.GetListQuery(singleElementList).FindLastIndex(0, 1, n => n == 10));
             Assert.Equal(-1, this.GetListQuery(singleElementList).FindLastIndex(0, 1, n => n == 99));
-            Assert.Throws<ArgumentOutOfRangeException>(() => this.GetListQuery(singleElementList).FindLastIndex(1, n => n == 10));
-            Assert.Throws<ArgumentOutOfRangeException>(() => this.GetListQuery(singleElementList).FindLastIndex(1, 1, n => n == 10));
+            AssertExtensions.Throws<ArgumentOutOfRangeException>("startIndex", () => this.GetListQuery(singleElementList).FindLastIndex(1, n => n == 10));
+            AssertExtensions.Throws<ArgumentOutOfRangeException>("startIndex", () => this.GetListQuery(singleElementList).FindLastIndex(1, 1, n => n == 10));
+            AssertExtensions.Throws<ArgumentOutOfRangeException>("count", () => this.GetListQuery(singleElementList).FindLastIndex(0, 2, n => n == 10));
 
             ImmutableList<int> multipleElementList = ImmutableList.Create(1, 2, 3, 4);
             Assert.Equal(2, this.GetListQuery(multipleElementList).FindLastIndex(3, 4, n => n == 3));
-            Assert.Throws<ArgumentOutOfRangeException>(() => this.GetListQuery(multipleElementList).FindLastIndex(4, n => n == 1));
-            Assert.Throws<ArgumentOutOfRangeException>(() => this.GetListQuery(multipleElementList).FindLastIndex(4, 1, n => n == 1));
-            Assert.Throws<ArgumentOutOfRangeException>(() => this.GetListQuery(multipleElementList).FindLastIndex(4, 4, n => n == 1));
+            AssertExtensions.Throws<ArgumentOutOfRangeException>("startIndex", () => this.GetListQuery(multipleElementList).FindLastIndex(4, n => n == 1));
+            AssertExtensions.Throws<ArgumentOutOfRangeException>("startIndex", () => this.GetListQuery(multipleElementList).FindLastIndex(2, 4, n => n == 1));
+            AssertExtensions.Throws<ArgumentOutOfRangeException>("startIndex", () => this.GetListQuery(multipleElementList).FindLastIndex(4, 1, n => n == 1));
+            AssertExtensions.Throws<ArgumentOutOfRangeException>("startIndex", () => this.GetListQuery(multipleElementList).FindLastIndex(4, 4, n => n == 1));
+            AssertExtensions.Throws<ArgumentOutOfRangeException>("count", () => this.GetListQuery(multipleElementList).FindLastIndex(3, 5, n => n == 1));
 
             // Create a list with contents: 100,101,102,103,104,100,101,102,103,104
             ImmutableList<int> list = ImmutableList<int>.Empty.AddRange(Enumerable.Range(100, 5).Concat(Enumerable.Range(100, 5)));
diff --git a/src/libraries/System.Collections.Immutable/tests/IndexOfTests.cs b/src/libraries/System.Collections.Immutable/tests/IndexOfTests.cs
index ed15b40f361637..d41ef7224a8ede 100644
--- a/src/libraries/System.Collections.Immutable/tests/IndexOfTests.cs
+++ b/src/libraries/System.Collections.Immutable/tests/IndexOfTests.cs
@@ -85,26 +85,29 @@ public static void LastIndexOfTest<TCollection>(
             Func<TCollection, int, IEqualityComparer<int>, int> lastIndexOfItemEQ,
             Func<TCollection, int, int, int> lastIndexOfItemIndex,
             Func<TCollection, int, int, int, int> lastIndexOfItemIndexCount,
-            Func<TCollection, int, int, int, IEqualityComparer<int>, int> lastIndexOfItemIndexCountEQ)
+            Func<TCollection, int, int, int, IEqualityComparer<int>, int> lastIndexOfItemIndexCountEQ,
+            string expectedIndexParamName,
+            string expectedCountParamName)
         {
             TCollection emptyCollection = factory(new int[0]);
             TCollection singleCollection = factory(new[] { 10 });
             TCollection collection1256 = factory(new[] { 1, 2, 5, 6 });
 
-            Assert.Throws<ArgumentOutOfRangeException>(() => lastIndexOfItemIndexCountEQ(emptyCollection, 100, 1, 1, EqualityComparer<int>.Default));
-            Assert.Throws<ArgumentOutOfRangeException>(() => lastIndexOfItemIndexCountEQ(emptyCollection, 100, -1, 1, EqualityComparer<int>.Default));
-            Assert.Throws<ArgumentOutOfRangeException>(() => lastIndexOfItemIndexCountEQ(singleCollection, 100, 1, 1, EqualityComparer<int>.Default));
-            Assert.Throws<ArgumentOutOfRangeException>(() => lastIndexOfItemIndexCountEQ(singleCollection, 100, -1, 1, EqualityComparer<int>.Default));
-            Assert.Throws<ArgumentOutOfRangeException>(() => lastIndexOfItemIndexCountEQ(collection1256, 100, 1, 20, EqualityComparer<int>.Default));
-            Assert.Throws<ArgumentOutOfRangeException>(() => lastIndexOfItemIndexCountEQ(collection1256, 100, 1, -1, EqualityComparer<int>.Default));
-            Assert.Throws<ArgumentOutOfRangeException>(() => lastIndexOfItemIndexCountEQ(emptyCollection, 100, 1, 1, new CustomComparer(50)));
-            Assert.Throws<ArgumentOutOfRangeException>(() => lastIndexOfItemIndexCountEQ(emptyCollection, 100, -1, 1, new CustomComparer(50)));
-            Assert.Throws<ArgumentOutOfRangeException>(() => lastIndexOfItemIndexCountEQ(singleCollection, 100, 1, 1, new CustomComparer(50)));
-            Assert.Throws<ArgumentOutOfRangeException>(() => lastIndexOfItemIndexCountEQ(singleCollection, 100, -1, 1, new CustomComparer(50)));
-            Assert.Throws<ArgumentOutOfRangeException>(() => lastIndexOfItemIndexCountEQ(collection1256, 100, 1, 20, new CustomComparer(1)));
-            Assert.Throws<ArgumentOutOfRangeException>(() => lastIndexOfItemIndexCountEQ(collection1256, 100, 1, -1, new CustomComparer(1)));
-            Assert.Throws<ArgumentOutOfRangeException>(() => lastIndexOfItemIndex(collection1256, 2, 5));
-            Assert.Throws<ArgumentOutOfRangeException>(() => lastIndexOfItemIndexCountEQ(collection1256, 6, 4, 4, EqualityComparer<int>.Default));
+            AssertExtensions.Throws<ArgumentOutOfRangeException>(expectedIndexParamName, () => lastIndexOfItemIndexCountEQ(emptyCollection, 100, 1, 1, EqualityComparer<int>.Default));
+            AssertExtensions.Throws<ArgumentOutOfRangeException>(expectedIndexParamName, () => lastIndexOfItemIndexCountEQ(emptyCollection, 100, -1, 1, EqualityComparer<int>.Default));
+            AssertExtensions.Throws<ArgumentOutOfRangeException>(expectedIndexParamName, () => lastIndexOfItemIndexCountEQ(singleCollection, 100, 1, 1, EqualityComparer<int>.Default));
+            AssertExtensions.Throws<ArgumentOutOfRangeException>(expectedIndexParamName, () => lastIndexOfItemIndexCountEQ(singleCollection, 100, -1, 1, EqualityComparer<int>.Default));
+            AssertExtensions.Throws<ArgumentOutOfRangeException>(expectedCountParamName, () => lastIndexOfItemIndexCountEQ(collection1256, 100, 1, 20, EqualityComparer<int>.Default));
+            AssertExtensions.Throws<ArgumentOutOfRangeException>(expectedCountParamName, () => lastIndexOfItemIndexCountEQ(collection1256, 100, 1, -1, EqualityComparer<int>.Default));
+            AssertExtensions.Throws<ArgumentOutOfRangeException>(expectedIndexParamName, () => lastIndexOfItemIndexCountEQ(emptyCollection, 100, 1, 1, new CustomComparer(50)));
+            AssertExtensions.Throws<ArgumentOutOfRangeException>(expectedIndexParamName, () => lastIndexOfItemIndexCountEQ(emptyCollection, 100, -1, 1, new CustomComparer(50)));
+            AssertExtensions.Throws<ArgumentOutOfRangeException>(expectedIndexParamName, () => lastIndexOfItemIndexCountEQ(singleCollection, 100, 1, 1, new CustomComparer(50)));
+            AssertExtensions.Throws<ArgumentOutOfRangeException>(expectedIndexParamName, () => lastIndexOfItemIndexCountEQ(singleCollection, 100, -1, 1, new CustomComparer(50)));
+            AssertExtensions.Throws<ArgumentOutOfRangeException>(expectedCountParamName, () => lastIndexOfItemIndexCountEQ(collection1256, 100, 1, 20, new CustomComparer(1)));
+            AssertExtensions.Throws<ArgumentOutOfRangeException>(expectedCountParamName, () => lastIndexOfItemIndexCountEQ(collection1256, 100, 1, -1, new CustomComparer(1)));
+            AssertExtensions.Throws<ArgumentOutOfRangeException>(expectedIndexParamName, () => lastIndexOfItemIndex(collection1256, 2, 5));
+            AssertExtensions.Throws<ArgumentOutOfRangeException>(expectedCountParamName, () => lastIndexOfItemIndexCountEQ(collection1256, 6, 2, 4, EqualityComparer<int>.Default));
+            AssertExtensions.Throws<ArgumentOutOfRangeException>(expectedIndexParamName, () => lastIndexOfItemIndexCountEQ(collection1256, 6, 4, 4, EqualityComparer<int>.Default));
 
             Assert.Equal(-1, lastIndexOfItem(emptyCollection, 5));
             Assert.Equal(-1, lastIndexOfItemEQ(emptyCollection, 5, EqualityComparer<int>.Default));