diff --git a/Octokit.Tests.Conventions/Exception/ParameterCountMismatchException.cs b/Octokit.Tests.Conventions/Exception/ParameterCountMismatchException.cs
new file mode 100644
index 00000000..331673d9
--- /dev/null
+++ b/Octokit.Tests.Conventions/Exception/ParameterCountMismatchException.cs
@@ -0,0 +1,33 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Reflection;
+using System.Runtime.Serialization;
+
+namespace Octokit.Tests.Conventions
+{
+    public class ParameterCountMismatchException : Exception
+    {
+        public ParameterCountMismatchException(MethodInfo method, IEnumerable<ParameterInfo> expected, IEnumerable<ParameterInfo> actual)
+            : base(CreateMessage(method, expected, actual)) { }
+
+        public ParameterCountMismatchException(MethodInfo method, IEnumerable<ParameterInfo> expected, IEnumerable<ParameterInfo> actual, Exception innerException)
+            : base(CreateMessage(method, expected, actual), innerException) { }
+
+        protected ParameterCountMismatchException(SerializationInfo info, StreamingContext context)
+            : base(info, context) { }
+
+        static string CreateMethodSignature(IEnumerable<ParameterInfo> parameters)
+        {
+            return String.Join(",", parameters.Select(p => String.Format("{0} {1}", p.ParameterType.Name, p.Name)));
+        }
+
+        static string CreateMessage(MethodInfo method, IEnumerable<ParameterInfo> expected, IEnumerable<ParameterInfo> actual)
+        {
+            var expectedMethodSignature = CreateMethodSignature(expected);
+            var actualMethodSignature = CreateMethodSignature(actual);
+
+            return String.Format("Method signature for {0}.{1} must be ({2}) but is ({3})", method.DeclaringType.Name, method.Name, expectedMethodSignature, actualMethodSignature);
+        }
+    }
+}
\ 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 8caa28f7..65a39e82 100644
--- a/Octokit.Tests.Conventions/Octokit.Tests.Conventions.csproj
+++ b/Octokit.Tests.Conventions/Octokit.Tests.Conventions.csproj
@@ -53,6 +53,7 @@
     <Compile Include="Exception\InterfaceHasAdditionalMethodsException.cs" />
     <Compile Include="Exception\InterfaceMissingMethodsException.cs" />
     <Compile Include="Exception\InterfaceNotFoundException.cs" />
+    <Compile Include="Exception\ParameterCountMismatchException.cs" />
     <Compile Include="Exception\ReturnValueMismatchException.cs" />
     <Compile Include="Properties\AssemblyInfo.cs" />
     <Compile Include="SyncObservableClients.cs" />
diff --git a/Octokit.Tests.Conventions/SyncObservableClients.cs b/Octokit.Tests.Conventions/SyncObservableClients.cs
index c78eb4cd..17d4a451 100644
--- a/Octokit.Tests.Conventions/SyncObservableClients.cs
+++ b/Octokit.Tests.Conventions/SyncObservableClients.cs
@@ -93,7 +93,12 @@ namespace Octokit.Tests.Conventions
         {
             var mainParameters = mainMethod.GetParametersOrdered();
             var observableParameters = observableMethod.GetParametersOrdered();
-            Assert.Equal(mainParameters.Length, observableParameters.Length);
+
+            if (mainParameters.Length != observableParameters.Length)
+            {
+                throw new ParameterCountMismatchException(observableMethod, mainParameters, observableParameters);
+            }
+
             int index = 0;
             foreach(var mainParameter in mainParameters)
             {