diff --git a/eng/tools/RepoTasks/RemoveSharedFrameworkDependencies.cs b/eng/tools/RepoTasks/RemoveSharedFrameworkDependencies.cs
index e29e25581607..6f42d05e78c5 100644
--- a/eng/tools/RepoTasks/RemoveSharedFrameworkDependencies.cs
+++ b/eng/tools/RepoTasks/RemoveSharedFrameworkDependencies.cs
@@ -64,12 +64,17 @@ private void FilterDependencies(string targetPath, ISet<string> dependencyToRemo
                     var updatedGroup = new PackageDependencyGroup(group.TargetFramework, packages);
                     foreach (var dependency in group.Packages)
                     {
-                        if (dependencyToRemove.Contains(dependency.Id))
+                        // Hack to temporarily avoid using ISet.Contains
+                        if (!dependencyToRemove.Add(dependency.Id))
                         {
                             referencesFrameworkOnlyAssembly = true;
                             Log.LogMessage($"  Remove dependency on '{dependency.Id}'");
                             continue;
                         }
+                        else
+                        {
+                            dependencyToRemove.Remove(dependency.Id);
+                        }
 
                         packages.Add(dependency);
                     }
@@ -107,4 +112,4 @@ private void FilterDependencies(string targetPath, ISet<string> dependencyToRemo
             }
         }
     }
-}
+}
\ No newline at end of file
diff --git a/src/Identity/Specification.Tests/src/UserManagerSpecificationTests.cs b/src/Identity/Specification.Tests/src/UserManagerSpecificationTests.cs
index 317f6ee93b13..4031bf5f2ba9 100644
--- a/src/Identity/Specification.Tests/src/UserManagerSpecificationTests.cs
+++ b/src/Identity/Specification.Tests/src/UserManagerSpecificationTests.cs
@@ -581,9 +581,9 @@ public async Task CanCreateUserAddLogin()
         var logins = await manager.GetLoginsAsync(user);
         Assert.NotNull(logins);
         Assert.Single(logins);
-        Assert.Equal(provider, logins.First().LoginProvider);
-        Assert.Equal(providerKey, logins.First().ProviderKey);
-        Assert.Equal(display, logins.First().ProviderDisplayName);
+        Assert.Equal(provider, logins[0].LoginProvider);
+        Assert.Equal(providerKey, logins[0].ProviderKey);
+        Assert.Equal(display, logins[0].ProviderDisplayName);
     }
 
     /// <summary>
@@ -644,9 +644,9 @@ public async Task CanCreateUserAddRemoveLogin()
         var logins = await manager.GetLoginsAsync(user);
         Assert.NotNull(logins);
         Assert.Single(logins);
-        Assert.Equal(login.LoginProvider, logins.Last().LoginProvider);
-        Assert.Equal(login.ProviderKey, logins.Last().ProviderKey);
-        Assert.Equal(login.ProviderDisplayName, logins.Last().ProviderDisplayName);
+        Assert.Equal(login.LoginProvider, logins[^1].LoginProvider);
+        Assert.Equal(login.ProviderKey, logins[^1].ProviderKey);
+        Assert.Equal(login.ProviderDisplayName, logins[^1].ProviderDisplayName);
         var stamp = await manager.GetSecurityStampAsync(user);
         IdentityResultAssert.IsSuccess(await manager.RemoveLoginAsync(user, login.LoginProvider, login.ProviderKey));
         Assert.Null(await manager.FindByLoginAsync(login.LoginProvider, login.ProviderKey));
@@ -772,11 +772,11 @@ public async Task CanReplaceUserClaim()
         var userClaims = await manager.GetClaimsAsync(user);
         Assert.Equal(1, userClaims.Count);
         Claim claim = new Claim("c", "b");
-        Claim oldClaim = userClaims.FirstOrDefault();
+        Claim oldClaim = userClaims.Count == 0 ? null : userClaims[0];
         IdentityResultAssert.IsSuccess(await manager.ReplaceClaimAsync(user, oldClaim, claim));
         var newUserClaims = await manager.GetClaimsAsync(user);
         Assert.Equal(1, newUserClaims.Count);
-        Claim newClaim = newUserClaims.FirstOrDefault();
+        Claim newClaim = newUserClaims.Count == 0 ? null : newUserClaims[0];
         Assert.Equal(claim.Type, newClaim.Type);
         Assert.Equal(claim.Value, newClaim.Value);
     }
@@ -800,16 +800,16 @@ public async Task ReplaceUserClaimOnlyAffectsUser()
         var userClaims2 = await manager.GetClaimsAsync(user);
         Assert.Equal(1, userClaims2.Count);
         Claim claim = new Claim("c", "b");
-        Claim oldClaim = userClaims.FirstOrDefault();
+        Claim oldClaim = userClaims.Count == 0 ? null : userClaims[0];
         IdentityResultAssert.IsSuccess(await manager.ReplaceClaimAsync(user, oldClaim, claim));
         var newUserClaims = await manager.GetClaimsAsync(user);
         Assert.Equal(1, newUserClaims.Count);
-        Claim newClaim = newUserClaims.FirstOrDefault();
+        Claim newClaim = newUserClaims.Count == 0 ? null : newUserClaims[0];
         Assert.Equal(claim.Type, newClaim.Type);
         Assert.Equal(claim.Value, newClaim.Value);
         userClaims2 = await manager.GetClaimsAsync(user2);
         Assert.Equal(1, userClaims2.Count);
-        Claim oldClaim2 = userClaims2.FirstOrDefault();
+        Claim oldClaim2 = userClaims2.Count == 0 ? null : userClaims2[0];
         Assert.Equal("c", oldClaim2.Type);
         Assert.Equal("a", oldClaim2.Value);
     }
diff --git a/src/Mvc/Mvc.Core/src/ApplicationModels/ActionAttributeRouteModel.cs b/src/Mvc/Mvc.Core/src/ApplicationModels/ActionAttributeRouteModel.cs
index 235ac3583fa0..5afa959e0fb5 100644
--- a/src/Mvc/Mvc.Core/src/ApplicationModels/ActionAttributeRouteModel.cs
+++ b/src/Mvc/Mvc.Core/src/ApplicationModels/ActionAttributeRouteModel.cs
@@ -31,7 +31,7 @@ public static IEnumerable<SelectorModel> FlattenSelectors(ActionModel actionMode
             //
             // This is fragile wrt application model customizing the data - but no one has
             // run into an issue with this and its pretty esoteric.
-            additionalSelector = new SelectorModel(actionModel.Controller.Selectors.First());
+            additionalSelector = new SelectorModel(actionModel.Controller.Selectors[0]);
             additionalSelector.AttributeRouteModel = null;
 
             for (var i = additionalSelector.ActionConstraints.Count - 1; i >= 0; i--)
diff --git a/src/Servers/Kestrel/Core/src/KestrelServerOptions.cs b/src/Servers/Kestrel/Core/src/KestrelServerOptions.cs
index c2670be70067..f16b35437001 100644
--- a/src/Servers/Kestrel/Core/src/KestrelServerOptions.cs
+++ b/src/Servers/Kestrel/Core/src/KestrelServerOptions.cs
@@ -2,7 +2,6 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 
 using System.Diagnostics;
-using System.Linq;
 using System.Net;
 using System.Security.Cryptography.X509Certificates;
 using System.Text;
@@ -376,9 +375,9 @@ internal void Serialize(Utf8JsonWriter writer)
     {
         try
         {
-            var cert = CertificateManager.Instance.ListCertificates(StoreName.My, StoreLocation.CurrentUser, isValid: true, requireExportable: false)
-                .FirstOrDefault();
+            var certs = CertificateManager.Instance.ListCertificates(StoreName.My, StoreLocation.CurrentUser, isValid: true, requireExportable: false);
 
+            var cert = certs.Count > 0 ? certs[0] : null;
             if (cert is null)
             {
                 logger.UnableToLocateDevelopmentCertificate();