diff --git a/Upsilon/BaseTypes/UserData/UserData.cs b/Upsilon/BaseTypes/UserData/UserData.cs
index e2300ec..2230647 100644
--- a/Upsilon/BaseTypes/UserData/UserData.cs
+++ b/Upsilon/BaseTypes/UserData/UserData.cs
@@ -48,5 +48,10 @@ namespace Upsilon.BaseTypes.UserData
         {
             return _typeInfo.BinaryOperator(Value, par1, op, par2);
         }
+
+        public (LuaType Type, bool Failed) UnaryOperator(LuaType par1, OperatorType op)
+        {
+            return _typeInfo.UnaryOperator(Value, par1, op);
+        }
     }
 }
\ No newline at end of file
diff --git a/Upsilon/BaseTypes/UserData/UserDataType.cs b/Upsilon/BaseTypes/UserData/UserDataType.cs
index 02e25cf..d91ea5f 100644
--- a/Upsilon/BaseTypes/UserData/UserDataType.cs
+++ b/Upsilon/BaseTypes/UserData/UserDataType.cs
@@ -82,5 +82,15 @@ namespace Upsilon.BaseTypes.UserData
 
             return (method.Invoke(value, new[] {par1.ToCSharpObject(), par2.ToCSharpObject()}).ToLuaType(), false);
         }
+        public (LuaType Type, bool Failed) UnaryOperator(object value, LuaType par1, OperatorType op)
+        {
+            var method = OperatorHandler.GetUnaryOperator(op, par1.GetCSharpType());
+            if (method == null)
+            {
+                return (new LuaNull(), true);
+            }
+
+            return (method.Invoke(value, new[] {par1.ToCSharpObject()}).ToLuaType(), false);
+        }
     }
 }
\ No newline at end of file
diff --git a/Upsilon/Binder/BoundUnaryOperator.cs b/Upsilon/Binder/BoundUnaryOperator.cs
index 2caa6e0..55cb7d2 100644
--- a/Upsilon/Binder/BoundUnaryOperator.cs
+++ b/Upsilon/Binder/BoundUnaryOperator.cs
@@ -50,6 +50,8 @@ namespace Upsilon.Binder
                     throw new Exception("Unknown unary operator token: " + operatorToken);
             }
 
+            if (inType == Type.Unknown)
+                return _operators.FirstOrDefault(op => op.Kind == kind);
             return _operators.FirstOrDefault(op => op.Kind == kind && op.InType == inType);
         }
     }
diff --git a/Upsilon/Evaluator/Evaluator.cs b/Upsilon/Evaluator/Evaluator.cs
index f67c26d..43e2063 100644
--- a/Upsilon/Evaluator/Evaluator.cs
+++ b/Upsilon/Evaluator/Evaluator.cs
@@ -165,9 +165,28 @@ namespace Upsilon.Evaluator
                 case BoundUnaryOperator.OperatorKind.Identity:
                     return operand;
                 case BoundUnaryOperator.OperatorKind.Negation:
-                    return -((Number)operand);
+                    if (operand.Type == Type.Number)
+                        return -((Number)operand);
+                    else if (operand.Type == Type.UserData)
+                    {
+                        var ud = (UserData) operand;
+                        var (type, failed) = ud.UnaryOperator(operand, OperatorType.UnaryNegation);
+                        if (failed) goto default;
+                        return type;
+                    }
+                    goto default;
                 case BoundUnaryOperator.OperatorKind.LogicalNegation:
-                    return !(LuaBoolean) operand;
+                    if (operand.Type == Type.Boolean)
+                        return !(LuaBoolean) operand;
+                    else if (operand.Type == Type.UserData)
+                    {
+                        var ud = (UserData) operand;
+                        var (type, failed) = ud.UnaryOperator(operand, OperatorType.LogicalNot);
+                        if (failed) goto default;
+                        return type;
+                    }
+                    goto default;
+
                 default:
                     throw new Exception("Invalid Unary Operator: " + e.Operator.Kind);
             }
diff --git a/UpsilonTests/UserDataOperatorTests.cs b/UpsilonTests/UserDataOperatorTests.cs
index 04f0e2a..17a8925 100644
--- a/UpsilonTests/UserDataOperatorTests.cs
+++ b/UpsilonTests/UserDataOperatorTests.cs
@@ -46,6 +46,11 @@ namespace UpsilonTests
                 return new UserDataHelper(a.Value - b.Value);
             }
 
+            public static UserDataHelper operator -(UserDataHelper a)
+            {
+                return new UserDataHelper(-a.Value);
+            }
+
             public static UserDataHelper operator *(UserDataHelper a, UserDataHelper b)
             {
                 return new UserDataHelper(a.Value * b.Value);
@@ -145,5 +150,21 @@ end
             Assert.Equal(10, result.Value);
         }
 
+        [Fact]
+        public void TestNegation()
+        {
+            const string input = @"
+function negate(o1)
+    return -o1
+end
+";
+            var script = new Script(input);
+            Assert.Empty(script.Diagnostics.Messages);
+            var o1     = new UserDataHelper(100);
+            var result = script.EvaluateFunction<UserDataHelper>("negate", new object[] {o1});
+            Assert.Empty(script.Diagnostics.Messages);
+            Assert.Equal(-100, result.Value);
+        }
+
     }
 }
\ No newline at end of file