diff --git a/Octokit.Tests.Conventions/Exception/InterfaceMethodsMismatchException.cs b/Octokit.Tests.Conventions/Exception/InterfaceMethodsMismatchException.cs
new file mode 100644
index 00000000..dad28aee
--- /dev/null
+++ b/Octokit.Tests.Conventions/Exception/InterfaceMethodsMismatchException.cs
@@ -0,0 +1,42 @@
+using System;
+using System.Linq;
+using System.Reflection;
+using System.Runtime.Serialization;
+
+namespace Octokit.Tests.Conventions
+{
+    public class InterfaceMethodsMismatchException : Exception
+    {
+        public InterfaceMethodsMismatchException(Type observableType, Type clientInterface)
+            : base(CreateMessage(observableType, clientInterface)) { }
+
+        public InterfaceMethodsMismatchException(Type type,Type clientInterface, Exception innerException)
+            : base(CreateMessage(type, clientInterface), innerException) { }
+
+        protected InterfaceMethodsMismatchException(SerializationInfo info, StreamingContext context)
+            : base(info, context) { }
+
+        static string Format(ParameterInfo parameterInfo)
+        {
+            return String.Format("{0} {1}", parameterInfo.ParameterType.Name, parameterInfo.Name);
+        }
+
+        static string Format(MethodInfo methodInfo)
+        {
+            var parameters = methodInfo.GetParameters().Select(Format);
+
+            return String.Format("{0} {1}({2})", methodInfo.ReturnType, methodInfo.Name, String.Join(", ", parameters));
+        }
+
+        static string CreateMessage(Type observableInterface, Type clientInterface)
+        {
+            var mainMethods = clientInterface.GetMethodsOrdered();
+            var observableMethods = observableInterface.GetMethodsOrdered();
+
+            var formattedMainMethods = String.Join("\r\n", mainMethods.Select(Format).Select(m => String.Format(" - {0}", m)));
+            var formattedObservableMethods = String.Join("\r\n", observableMethods.Select(Format).Select(m => String.Format(" - {0}", m)));
+
+            return String.Format("There are some overloads which are confusing the convention tests. Check everything is okay in these types:\r\n{0}\r\n{2}\r\n{1}\r\n{3}", clientInterface.Name, observableInterface.Name, formattedMainMethods, formattedObservableMethods);
+        }
+    }
+}
\ No newline at end of file
diff --git a/Octokit.Tests.Conventions/Octokit.Tests.Conventions.csproj b/Octokit.Tests.Conventions/Octokit.Tests.Conventions.csproj
index f50961d5..096592b4 100644
--- a/Octokit.Tests.Conventions/Octokit.Tests.Conventions.csproj
+++ b/Octokit.Tests.Conventions/Octokit.Tests.Conventions.csproj
@@ -51,6 +51,7 @@
   <ItemGroup>
     <Compile Include="DebuggerDisplayOnModels.cs" />
     <Compile Include="Exception\InterfaceHasAdditionalMethodsException.cs" />
+    <Compile Include="Exception\InterfaceMethodsMismatchException.cs" />
     <Compile Include="Exception\InterfaceMissingMethodsException.cs" />
     <Compile Include="Exception\InterfaceNotFoundException.cs" />
     <Compile Include="Exception\ParameterCountMismatchException.cs" />
diff --git a/Octokit.Tests.Conventions/SyncObservableClients.cs b/Octokit.Tests.Conventions/SyncObservableClients.cs
index 4c296f64..2302f0f5 100644
--- a/Octokit.Tests.Conventions/SyncObservableClients.cs
+++ b/Octokit.Tests.Conventions/SyncObservableClients.cs
@@ -34,6 +34,11 @@ namespace Octokit.Tests.Conventions
                 throw new InterfaceHasAdditionalMethodsException(observableClient, additionalMethodsOnReactiveClient);
             }
 
+            if (mainNames.Count() != observableNames.Count())
+            {
+                throw new InterfaceMethodsMismatchException(observableClient, clientInterface);
+            }
+
             int index = 0;
             foreach(var mainMethod in mainMethods)
             {