diff --git a/UnitTests/InternetAddressListTypeConverterTests.cs b/UnitTests/InternetAddressListTypeConverterTests.cs
index 0785871332..5b312b5749 100644
--- a/UnitTests/InternetAddressListTypeConverterTests.cs
+++ b/UnitTests/InternetAddressListTypeConverterTests.cs
@@ -79,6 +79,7 @@ public void TestIsNotValid ()
 		{
 			var converter = TypeDescriptor.GetConverter (typeof (InternetAddressList));
 			Assert.That (converter.IsValid (""), Is.False);
+			Assert.That (converter.IsValid (5), Is.False);
 		}
 	}
 }
diff --git a/UnitTests/InternetAddressTypeConverterTests.cs b/UnitTests/InternetAddressTypeConverterTests.cs
index deb77dfa63..a8294a8e05 100644
--- a/UnitTests/InternetAddressTypeConverterTests.cs
+++ b/UnitTests/InternetAddressTypeConverterTests.cs
@@ -76,6 +76,7 @@ public void TestIsNotValid ()
 		{
 			var converter = TypeDescriptor.GetConverter (typeof (InternetAddress));
 			Assert.That (converter.IsValid (""), Is.False);
+			Assert.That (converter.IsValid (5), Is.False);
 		}
 	}
 }