diff --git a/EntityFramework.Functions.Tests/Examples/ModelDefinedFunctions.cs b/EntityFramework.Functions.Tests/Examples/ModelDefinedFunctions.cs
index 0d41739..f912c85 100644
--- a/EntityFramework.Functions.Tests/Examples/ModelDefinedFunctions.cs
+++ b/EntityFramework.Functions.Tests/Examples/ModelDefinedFunctions.cs
@@ -3,14 +3,26 @@
     using EntityFramework.Functions.Tests.Library.Examples;
 
     public static class ModelDefinedFunctions
-	{
-		[ModelDefinedFunction(nameof(FormatName), "EntityFramework.Functions.Tests.Examples",
+    {
+        [ModelDefinedFunction(nameof(FormatName), "EntityFramework.Functions.Tests.Examples",
             @"(CASE 
                 WHEN [Person].[Title] IS NOT NULL
                 THEN [Person].[Title] + N' ' 
                 ELSE N'' 
             END) + [Person].[FirstName] + N' ' + [Person].[LastName]")]
-		public static string FormatName(this Person person) =>
-		    $"{(person.Title == null ? string.Empty : person.Title + " ")}{person.FirstName} {person.LastName}";
-	}
-}
\ No newline at end of file
+        public static string FormatName(this Person person) =>
+            $"{(person.Title == null ? string.Empty : person.Title + " ")}{person.FirstName} {person.LastName}";
+
+        /*
+        <Function Name="ParseDouble" ReturnType="Edm.Double">
+            <Parameter Name="svalue" Type="Edm.String" />
+             <DefiningExpression>
+                cast(svalue as Edm.Double)
+             </DefiningExpression>
+         </Function>
+         */
+        [ModelDefinedFunction(nameof(ParseDouble), "EntityFramework.Functions.Tests.Examples", @"cast(svalue as Edm.Double)")]
+        public static double ParseDouble(this string svalue) => double.Parse(svalue);
+
+    }
+}
diff --git a/EntityFramework.Functions.Tests/UnitTests/FunctionTests.cs b/EntityFramework.Functions.Tests/UnitTests/FunctionTests.cs
index 5bd424c..be6dafe 100644
--- a/EntityFramework.Functions.Tests/UnitTests/FunctionTests.cs
+++ b/EntityFramework.Functions.Tests/UnitTests/FunctionTests.cs
@@ -235,5 +235,17 @@ public void ModelDefinedFunctionInLinqTest()
                 Assert.AreEqual(employeeData.employee.FormatName(), employeeData.formatted);
             }
         }
+
+        [TestMethod]
+        public void ModelDefinedFunctionInLinqTest2()
+        {
+            using (AdventureWorks database = new AdventureWorks())
+            {
+                var result = (from employee in database.Persons
+                                let formatted = "23.00".ParseDouble()
+                                select formatted).FirstOrDefault();
+                Assert.AreEqual(23.00, result);
+            }
+        }
     }
 }
diff --git a/EntityFramework.Functions/Function.DbModel.cs b/EntityFramework.Functions/Function.DbModel.cs
index 100ce0d..8f027ad 100644
--- a/EntityFramework.Functions/Function.DbModel.cs
+++ b/EntityFramework.Functions/Function.DbModel.cs
@@ -492,7 +492,7 @@ private static IList<FunctionParameter> GetStoreReturnParameters(
                 if (modelReturnParameterComplexType != null)
                 {
                     storeReturnParameterRowType = RowType.Create(
-                        modelReturnParameterComplexType.Properties.Select(property => 
+                        modelReturnParameterComplexType.Properties.Select(property =>
                             EdmProperty.Create(property.Name, model.ProviderManifest.GetStoreType(property.TypeUsage))),
                         null);
                 }
@@ -557,12 +557,34 @@ private static IList<FunctionParameter> GetModelParametersForModelDefinedFunctio
             this DbModel model, MethodInfo methodInfo)
         {
             ParameterInfo[] parameters = methodInfo.GetParameters().ToArray();
-            return parameters
-                .Select((parameterInfo) => FunctionParameter.Create(
-                    parameterInfo.GetCustomAttribute<ParameterAttribute>()?.Name ?? parameterInfo.Name,
-                    model.GetModelStructualType(parameterInfo.ParameterType, methodInfo),
-                    ParameterMode.In))
-                .ToArray();
+            return parameters.Select(
+                (parameterInfo) =>
+                {
+                    EdmType type = model.GetModelPrimitiveType(parameterInfo.ParameterType, methodInfo);
+                    if (type == null)
+                    {
+                        type = model.GetModelComplexType(parameterInfo.ParameterType, methodInfo);
+                        if (type == null)
+                        {
+                            type = model.GetModelEntityType(parameterInfo.ParameterType, methodInfo);
+                            if (type == null)
+                            {
+                                type = model.GetModelStructualType(parameterInfo.ParameterType, methodInfo);
+                                if (type == null)
+                                {
+                                    throw new NotSupportedException(
+                                        $"{parameterInfo.ParameterType.FullName} for method {methodInfo.Name} is "
+                                        + "not supported in conceptual model");
+                                }
+                            }
+                        }
+                    }
+
+                    return FunctionParameter.Create(parameterInfo.GetCustomAttribute<ParameterAttribute>()?.Name ?? parameterInfo.Name,
+                                                    type,
+                                                    ParameterMode.In);
+                }
+                ).ToArray();
         }
 
         private static IList<FunctionParameter> GetModelReturnParameters(
@@ -694,11 +716,11 @@ private static PrimitiveType GetModelPrimitiveType(this DbModel model, Type clrT
             PrimitiveType modelPrimitiveType = PrimitiveType
                 .GetEdmPrimitiveTypes()
                 .FirstOrDefault(primitiveType => primitiveType.ClrEquivalentType == clrType);
-            if (modelPrimitiveType == null)
-            {
-                throw new NotSupportedException(
-                    $"Type {nameof(clrType.FullName)} in method {methodInfo.Name} is not supported in conceptual model.");
-            }
+            //if (modelPrimitiveType == null)
+            //{
+            //    throw new NotSupportedException(
+            //        $"Type {nameof(clrType.FullName)} in method {methodInfo.Name} is not supported in conceptual model.");
+            //}
 
             return modelPrimitiveType;
         }
@@ -717,8 +739,10 @@ private static StructuralType GetModelStructualType(this DbModel model, Type clr
                 return complexType;
             }
 
-            throw new NotSupportedException(
-                $"{clrType.FullName} for method {methodInfo.Name} is not supported in conceptual model as a structural type.");
+            return default(StructuralType);
+
+            //throw new NotSupportedException(
+            //    $"{clrType.FullName} for method {methodInfo.Name} is not supported in conceptual model as a structural type.");
         }
 
         private static EntityType GetModelEntityType(this DbModel model, Type clrType, MethodInfo methodInfo)