diff --git a/src/MemoryPack.Generator/MemoryPackGenerator.Emitter.cs b/src/MemoryPack.Generator/MemoryPackGenerator.Emitter.cs
index 4246386..c264cf1 100644
--- a/src/MemoryPack.Generator/MemoryPackGenerator.Emitter.cs
+++ b/src/MemoryPack.Generator/MemoryPackGenerator.Emitter.cs
@@ -1376,12 +1376,12 @@ string EmitConstantValue(object? constantValue)
                 string x => $"\"{x}\"",
                 char x => $"'{x}'",
                 float x => $"{x}f",
-                decimal x => $"{x}D",
+                decimal x => $"{x}M",
                 bool x => x ? "true" : "false",
                 _ => constantValue.ToString()
             };
         }
-        return "null";
+        return "default!";
     }
 
     string EmitExpression(ExpressionSyntax expression)
@@ -1392,13 +1392,13 @@ string EmitExpression(ExpressionSyntax expression)
             {
                 var memberAccess = (MemberAccessExpressionSyntax)expression;
                 var memberSymbol = semanticModel.GetSymbolInfo(memberAccess.Name).Symbol;
-                if (memberSymbol is INamedTypeSymbol namedTypeSymbol && namedTypeSymbol.TypeKind == TypeKind.Enum)
+                if (memberSymbol is INamedTypeSymbol { TypeKind: TypeKind.Enum } namedTypeSymbol)
                 {
-                    return $"{GetTypeFullName(namedTypeSymbol, semanticModel)}.{memberAccess.Name}";
+                    return $"{GetTypeFullName(namedTypeSymbol)}.{memberAccess.Name}";
                 }
-                if (memberSymbol is IFieldSymbol fieldSymbol && fieldSymbol.ContainingType.TypeKind == TypeKind.Enum)
+                if (memberSymbol is IFieldSymbol { Type.TypeKind: TypeKind.Enum } fieldSymbol)
                 {
-                    return $"{GetTypeFullName(fieldSymbol.ContainingType, semanticModel)}.{fieldSymbol.Name}";
+                    return $"{GetTypeFullName(fieldSymbol.Type)}.{fieldSymbol.Name}";
                 }
                 break;
             }
@@ -1412,7 +1412,7 @@ string EmitExpression(ExpressionSyntax expression)
                     var arguments = string.Join(", ",
                         objectCreation.ArgumentList?.Arguments.Select(arg =>
                             EmitExpression(arg.Expression)) ?? Enumerable.Empty<string>());
-                    return $"new {x.ToDisplayString(SymbolDisplayFormat.FullyQualifiedFormat)}({arguments})";
+                    return $"new {GetTypeFullName(x)}({arguments})";
                 }
                 break;
             }
@@ -1426,10 +1426,15 @@ string EmitExpression(ExpressionSyntax expression)
         return expression.ToString();
     }
 
-    string GetTypeFullName(ITypeSymbol typeSymbol, SemanticModel semanticModel)
+    static string GetTypeFullName(ITypeSymbol typeSymbol)
     {
-        var containingType = typeSymbol.ContainingType;
-        var containingTypeFullName = containingType == null ? "" : GetTypeFullName(containingType, semanticModel) + ".";
-        return containingTypeFullName + typeSymbol.ToDisplayString(SymbolDisplayFormat.FullyQualifiedFormat);
+        if (typeSymbol.ContainingType is { } containingType)
+        {
+            // nested type
+            var containingTypeFullName = containingType.ToDisplayString(SymbolDisplayFormat.FullyQualifiedFormat);
+            var typeName = typeSymbol.ToDisplayString(SymbolDisplayFormat.MinimallyQualifiedFormat);
+            return $"{containingTypeFullName}.{typeName}";
+        }
+        return typeSymbol.ToDisplayString(SymbolDisplayFormat.FullyQualifiedFormat);
     }
 }
diff --git a/tests/MemoryPack.Tests/Models/DefaultValues.cs b/tests/MemoryPack.Tests/Models/DefaultValues.cs
index ab878bc..c13aa0a 100644
--- a/tests/MemoryPack.Tests/Models/DefaultValues.cs
+++ b/tests/MemoryPack.Tests/Models/DefaultValues.cs
@@ -1,3 +1,4 @@
+using System;
 using System.Collections.Generic;
 
 namespace MemoryPack.Tests.Models;
@@ -26,14 +27,21 @@ partial class FieldDefaultValue
 [MemoryPackable]
 partial class PropertyDefaultValue
 {
+    internal enum NestedEnum
+    {
+        A, B
+    }
+
     public int X { get; set; }
     public int Y { get; set; } = 12345;
     public float Z { get; set; } = 678.9f;
     public string S { get; set; } = "aaaaaaaaa";
     public bool B { get; set; } = true;
     public List<string> Alpha { get; set; } = new List<string>(new HashSet<string>());
-    public TestEnum TestEnum { get; set; } = TestEnum.A;
+    public TestEnum E { get; set; } = TestEnum.A;
+    public NestedEnum E2 { get; set; } = NestedEnum.A;
     public (TestEnum, List<string>) Tuple { get; set; } = (TestEnum.A, new List<string>(new HashSet<string>()));
+    public DateTime Struct { get; set; } = default!;
 }
 
 [MemoryPackable]
@@ -44,14 +52,18 @@ partial class CtorParamDefaultValue
     public float Z;
     public string S;
     public bool B;
+    public decimal D;
+    public DateTime StructValue;
 
     [MemoryPackConstructor]
-    public CtorParamDefaultValue(int x, int y = 12345, float z = 678.9f, string s = "aaaaaa", bool b = true)
+    public CtorParamDefaultValue(int x, int y = 12345, float z = 678.9f, string s = "aaaaaa", bool b = true, decimal d = 99M, DateTime structValue = default)
     {
         X = x;
         Y = y;
         Z = z;
         S = s;
         B = b;
+        D = d;
+        StructValue = structValue;
     }
 }