diff --git a/Octokit.Tests/Clients/MilestonesClientTests.cs b/Octokit.Tests/Clients/MilestonesClientTests.cs
index fbfd8b3f..cecfa64d 100644
--- a/Octokit.Tests/Clients/MilestonesClientTests.cs
+++ b/Octokit.Tests/Clients/MilestonesClientTests.cs
@@ -30,7 +30,7 @@ namespace Octokit.Tests.Clients
 
                 await Assert.ThrowsAsync<ArgumentNullException>(() => client.Get(null, "name", 1));
                 await Assert.ThrowsAsync<ArgumentNullException>(() => client.Get("owner", null, 1));
-                await Assert.ThrowsAsync<ArgumentException>(() => client.Get(null, "", 1));
+                await Assert.ThrowsAsync<ArgumentNullException>(() => client.Get(null, "", 1));
                 await Assert.ThrowsAsync<ArgumentException>(() => client.Get("", null, 1));
             }
         }
diff --git a/Octokit.Tests/Clients/OrganizationMembersClientTests.cs b/Octokit.Tests/Clients/OrganizationMembersClientTests.cs
index d1040fb2..3bc42e51 100644
--- a/Octokit.Tests/Clients/OrganizationMembersClientTests.cs
+++ b/Octokit.Tests/Clients/OrganizationMembersClientTests.cs
@@ -135,7 +135,7 @@ namespace Octokit.Tests.Clients
                 var orgMembers = new OrganizationMembersClient(Substitute.For<IApiConnection>());
 
                 await Assert.ThrowsAsync<ArgumentNullException>(() => orgMembers.CheckMember(null, "username"));
-                await Assert.ThrowsAsync<ArgumentException>(() => orgMembers.CheckMember(null, ""));
+                await Assert.ThrowsAsync<ArgumentNullException>(() => orgMembers.CheckMember(null, ""));
                 await Assert.ThrowsAsync<ArgumentNullException>(() => orgMembers.CheckMember("org", null));
                 await Assert.ThrowsAsync<ArgumentException>(() => orgMembers.CheckMember("", null));
             }
diff --git a/Octokit.Tests/Clients/PullRequestReviewCommentsClientTests.cs b/Octokit.Tests/Clients/PullRequestReviewCommentsClientTests.cs
index c6318773..88499921 100644
--- a/Octokit.Tests/Clients/PullRequestReviewCommentsClientTests.cs
+++ b/Octokit.Tests/Clients/PullRequestReviewCommentsClientTests.cs
@@ -229,7 +229,7 @@ public class PullRequestReviewCommentsClientTests
             await Assert.ThrowsAsync<ArgumentException>(() => client.Create("", "fakeRepoName", 1, comment));
             await Assert.ThrowsAsync<ArgumentNullException>(() => client.Create("fakeOwner", null, 1, comment));
             await Assert.ThrowsAsync<ArgumentException>(() => client.Create("fakeOwner", "", 1, comment));
-            await Assert.ThrowsAsync<ArgumentException>(() => client.Create("fakeOwner", "fakeRepoName", 1, null));
+            await Assert.ThrowsAsync<ArgumentNullException>(() => client.Create("fakeOwner", "fakeRepoName", 1, null));
         }
     }
 
@@ -264,7 +264,7 @@ public class PullRequestReviewCommentsClientTests
             await Assert.ThrowsAsync<ArgumentException>(() => client.CreateReply("", "fakeRepoName", 1, comment));
             await Assert.ThrowsAsync<ArgumentNullException>(() => client.CreateReply("fakeOwner", null, 1, comment));
             await Assert.ThrowsAsync<ArgumentException>(() => client.CreateReply("fakeOwner", "", 1, comment));
-            await Assert.ThrowsAsync<ArgumentException>(() => client.CreateReply("fakeOwner", "fakeRepoName", 1, null));
+            await Assert.ThrowsAsync<ArgumentNullException>(() => client.CreateReply("fakeOwner", "fakeRepoName", 1, null));
         }
     }
 
diff --git a/Octokit.Tests/Clients/PullRequestsClientTests.cs b/Octokit.Tests/Clients/PullRequestsClientTests.cs
index 10dc9b3f..60dcd873 100644
--- a/Octokit.Tests/Clients/PullRequestsClientTests.cs
+++ b/Octokit.Tests/Clients/PullRequestsClientTests.cs
@@ -30,7 +30,7 @@ namespace Octokit.Tests.Clients
 
                 await Assert.ThrowsAsync<ArgumentNullException>(() => client.Get(null, "name", 1));
                 await Assert.ThrowsAsync<ArgumentNullException>(() => client.Get("owner", null, 1));
-                await Assert.ThrowsAsync<ArgumentException>(() => client.Get(null, "", 1));
+                await Assert.ThrowsAsync<ArgumentNullException>(() => client.Get(null, "", 1));
                 await Assert.ThrowsAsync<ArgumentException>(() => client.Get("", null, 1));
             }
         }
@@ -189,7 +189,7 @@ namespace Octokit.Tests.Clients
 
                 await Assert.ThrowsAsync<ArgumentNullException>(() => client.Merged(null, "name", 1));
                 await Assert.ThrowsAsync<ArgumentNullException>(() => client.Merged("owner", null, 1));
-                await Assert.ThrowsAsync<ArgumentException>(() => client.Merged(null, "", 1));
+                await Assert.ThrowsAsync<ArgumentNullException>(() => client.Merged(null, "", 1));
                 await Assert.ThrowsAsync<ArgumentException>(() => client.Merged("", null, 1));
             }
         }
@@ -216,7 +216,7 @@ namespace Octokit.Tests.Clients
 
                 await Assert.ThrowsAsync<ArgumentNullException>(() => client.Commits(null, "name", 1));
                 await Assert.ThrowsAsync<ArgumentNullException>(() => client.Commits("owner", null, 1));
-                await Assert.ThrowsAsync<ArgumentException>(() => client.Commits(null, "", 1));
+                await Assert.ThrowsAsync<ArgumentNullException>(() => client.Commits(null, "", 1));
                 await Assert.ThrowsAsync<ArgumentException>(() => client.Commits("", null, 1));
             }
         }