Fix custom options behaviour
diff --git a/src/ProtocolBuffers.Test/DynamicMessageTest.cs b/src/ProtocolBuffers.Test/DynamicMessageTest.cs
index 2f3fefa..69e2e6b 100644
--- a/src/ProtocolBuffers.Test/DynamicMessageTest.cs
+++ b/src/ProtocolBuffers.Test/DynamicMessageTest.cs
@@ -64,7 +64,7 @@
       try {
         builder.Build();
         Assert.Fail("Should have thrown exception.");
-      } catch (InvalidOperationException e) {
+      } catch (InvalidOperationException) {
         // Success.
       }
     }