diff --git a/Octokit.Tests/Reactive/ObservableIssuesClientTests.cs b/Octokit.Tests/Reactive/ObservableIssuesClientTests.cs
index d7bf8358..aa23f958 100644
--- a/Octokit.Tests/Reactive/ObservableIssuesClientTests.cs
+++ b/Octokit.Tests/Reactive/ObservableIssuesClientTests.cs
@@ -32,7 +32,7 @@ public class ObservableIssuesClientTests
 
             await Assert.ThrowsAsync<ArgumentNullException>(() => client.Get(null, "name", 1).ToTask());
             await Assert.ThrowsAsync<ArgumentNullException>(() => client.Get("owner", null, 1).ToTask());
-            await Assert.ThrowsAsync<ArgumentException>(() => client.Get(null, "", 1).ToTask());
+            await Assert.ThrowsAsync<ArgumentNullException>(() => client.Get(null, "", 1).ToTask());
             await Assert.ThrowsAsync<ArgumentException>(() => client.Get("", null, 1).ToTask());
         }
     }
diff --git a/Octokit.Tests/Reactive/ObservableMilestonesClientTests.cs b/Octokit.Tests/Reactive/ObservableMilestonesClientTests.cs
index 320d6a2c..fd4823ed 100644
--- a/Octokit.Tests/Reactive/ObservableMilestonesClientTests.cs
+++ b/Octokit.Tests/Reactive/ObservableMilestonesClientTests.cs
@@ -33,7 +33,7 @@ namespace Octokit.Tests.Reactive
 
                 await Assert.ThrowsAsync<ArgumentNullException>(() => client.Get(null, "name", 1).ToTask());
                 await Assert.ThrowsAsync<ArgumentNullException>(() => client.Get("owner", null, 1).ToTask());
-                await Assert.ThrowsAsync<ArgumentException>(() => client.Get(null, "", 1).ToTask());
+                await Assert.ThrowsAsync<ArgumentNullException>(() => client.Get(null, "", 1).ToTask());
                 await Assert.ThrowsAsync<ArgumentException>(() => client.Get("", null, 1).ToTask());
             }
         }
diff --git a/Octokit.Tests/Reactive/ObservablePullRequestsClientTests.cs b/Octokit.Tests/Reactive/ObservablePullRequestsClientTests.cs
index 68626854..8af603e2 100644
--- a/Octokit.Tests/Reactive/ObservablePullRequestsClientTests.cs
+++ b/Octokit.Tests/Reactive/ObservablePullRequestsClientTests.cs
@@ -34,7 +34,7 @@ namespace Octokit.Tests.Reactive
 
                 await Assert.ThrowsAsync<ArgumentNullException>(() => client.Get(null, "name", 1).ToTask());
                 await Assert.ThrowsAsync<ArgumentNullException>(() => client.Get("owner", null, 1).ToTask());
-                await Assert.ThrowsAsync<ArgumentException>(() => client.Get(null, "", 1).ToTask());
+                await Assert.ThrowsAsync<ArgumentNullException>(() => client.Get(null, "", 1).ToTask());
                 await Assert.ThrowsAsync<ArgumentException>(() => client.Get("", null, 1).ToTask());
             }
         }
@@ -270,7 +270,7 @@ namespace Octokit.Tests.Reactive
 
                 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));
             }
         }
@@ -309,7 +309,7 @@ namespace Octokit.Tests.Reactive
 
                 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));
             }
         }
diff --git a/Octokit.Tests/Reactive/ObservableStarredClientTests.cs b/Octokit.Tests/Reactive/ObservableStarredClientTests.cs
index 6c3afbdb..ea233f38 100644
--- a/Octokit.Tests/Reactive/ObservableStarredClientTests.cs
+++ b/Octokit.Tests/Reactive/ObservableStarredClientTests.cs
@@ -23,7 +23,7 @@ namespace Octokit.Tests.Reactive
             {
                 var client = new ObservableStarredClient(Substitute.For<IGitHubClient>());
 
-                await Assert.ThrowsAsync<ArgumentException>(() => client.GetAllStargazers(null, "name").ToTask());
+                await Assert.ThrowsAsync<ArgumentNullException>(() => client.GetAllStargazers(null, "name").ToTask());
                 await Assert.ThrowsAsync<ArgumentException>(() => client.GetAllStargazers("owner", null).ToTask());
             }
 
@@ -62,7 +62,7 @@ namespace Octokit.Tests.Reactive
             {
                 var client = new ObservableStarredClient(Substitute.For<IGitHubClient>());
 
-                await Assert.ThrowsAsync<ArgumentException>(() => client.GetAllForUser(null).ToTask());
+                await Assert.ThrowsAsync<ArgumentNullException>(() => client.GetAllForUser(null).ToTask());
             }
 
             [Fact]
@@ -85,7 +85,7 @@ namespace Octokit.Tests.Reactive
             {
                 var client = new ObservableStarredClient(Substitute.For<IGitHubClient>());
 
-                await Assert.ThrowsAsync<ArgumentException>(() => client.CheckStarred(null, "james").ToTask());
+                await Assert.ThrowsAsync<ArgumentNullException>(() => client.CheckStarred(null, "james").ToTask());
                 await Assert.ThrowsAsync<ArgumentException>(() => client.CheckStarred("james", null).ToTask());
             }
 
@@ -107,7 +107,7 @@ namespace Octokit.Tests.Reactive
             {
                 var client = new ObservableStarredClient(Substitute.For<IGitHubClient>());
 
-                await Assert.ThrowsAsync<ArgumentException>(() => client.StarRepo(null, "james").ToTask());
+                await Assert.ThrowsAsync<ArgumentNullException>(() => client.StarRepo(null, "james").ToTask());
                 await Assert.ThrowsAsync<ArgumentException>(() => client.StarRepo("james", null).ToTask());
             }
 
@@ -129,7 +129,7 @@ namespace Octokit.Tests.Reactive
             {
                 var client = new ObservableStarredClient(Substitute.For<IGitHubClient>());
 
-                await Assert.ThrowsAsync<ArgumentException>(() => client.RemoveStarFromRepo(null, "james").ToTask());
+                await Assert.ThrowsAsync<ArgumentNullException>(() => client.RemoveStarFromRepo(null, "james").ToTask());
                 await Assert.ThrowsAsync<ArgumentException>(() => client.RemoveStarFromRepo("james", null).ToTask());
             }