diff --git a/base.cpp b/base.cpp
index 0166a2d..bfd845a 100644
--- a/base.cpp
+++ b/base.cpp
@@ -21,6 +21,7 @@ typedef S64      SizeS;
 typedef float    F32;
 typedef double   F64;
 
+
 #define U64MAX UINT64_MAX
 #define U32MAX UINT32_MAX
 #define U16MAX UINT16_MAX
diff --git a/core_typechecking.cpp b/core_typechecking.cpp
index a6eb8bb..c8e1f5c 100644
--- a/core_typechecking.cpp
+++ b/core_typechecking.cpp
@@ -1234,6 +1234,11 @@ resolve_expr(Ast_Expr *ast, Resolve_Flag flags, Ast_Type *compound_context){
         }
 
         Ast_Type *type = name.type == type_type ? name.type_val : name.type;
+        type_complete(type);
+        if(type->size == 0){
+          compiler_error(node->pos, "Internal compiler error: calling SizeOf but the resulting size of type is obviously invalid suggesting that type was not completed properly");
+        }
+
         Value v = value_int(type->size);
         rewrite_into_const(node, Ast_Builtin, v);
         return operand_const_rvalue(v);
@@ -1265,8 +1270,16 @@ resolve_expr(Ast_Expr *ast, Resolve_Flag flags, Ast_Type *compound_context){
         Ast_Expr *expr = unpack_ast_call_expr_for_builtin(node);
         Operand name = resolve_expr(expr, inherit_flag(flags, AST_CANT_BE_NULL));
         node->kind = AST_ALIGN_OF;
-        if(!name.is_const) compiler_error(node->pos, "AlignOf requires a constant value");
+        if(!name.is_const) {
+          compiler_error(node->pos, "AlignOf requires a constant value");
+        }
+
         Ast_Type *type = name.type == type_type ? name.type_val : name.type;
+        type_complete(type);
+        if(type->size == 0){
+          compiler_error(node->pos, "Internal compiler error: calling SizeOf but the resulting size of type is obviously invalid suggesting that type was not completed properly");
+        }
+
         Value v = value_int(type->align);
         rewrite_into_const(node, Ast_Builtin, v);
         return operand_const_rvalue(v);
diff --git a/core_typechecking.h b/core_typechecking.h
index 19d54ce..81a470b 100644
--- a/core_typechecking.h
+++ b/core_typechecking.h
@@ -261,21 +261,33 @@ type_incomplete(Ast *ast){
   return result;
 }
 
+function void type_complete(Ast_Type *type);
 function void
 type_struct_complete(Ast_Type *type, Ast_Decl *node){
   assert(node->kind == AST_STRUCT);
   // @todo: compute size, alignement, offset !!!
   // @note: resolve all the struct members first
-  type->kind = TYPE_COMPLETING;
   Scratch scratch;
   Array<Ast_Resolved_Member> members = {scratch};
+  type->kind = TYPE_COMPLETING;
+  size_t members_size = 0;
   For(node->scope->decls){
     resolve_decl(it);
+    assert(it->type->kind != TYPE_INCOMPLETE);
+    assert(is_pow2(it->type->align));
+
     Ast_Resolved_Member m = {};
+    m.offset = type->size;
+    members_size += it->type->size;
+    type->align = max(type->align, it->type->align);
+    type->size = it->type->size + align_up(type->size, it->type->align);
+
     m.name = it->name;
     m.value = it->value;
     members.add(m);
   }
+  type->size = align_up(type->size, type->align);
+  type->padding = type->size - members_size;
   type->agg.members = members.tight_copy(pctx->perm);
   type->kind = TYPE_STRUCT;
 }
diff --git a/core_types.h b/core_types.h
index d3107c1..679f09f 100644
--- a/core_types.h
+++ b/core_types.h
@@ -63,6 +63,7 @@ union{                           \
   Ast_Type *type_val;            \
 };
 #define INLINE_VALUE_FIELDS union{Value value; struct{VALUE_FIELDS};}
+#define ARRAY_SIZE_SLICE (-1)
 struct Value{VALUE_FIELDS};
 
 struct Ast;
@@ -74,13 +75,13 @@ struct Ast_Resolved_Member{
   INLINE_VALUE_FIELDS;
 };
 
-#define ARRAY_SIZE_SLICE (-1)
 struct Ast_Type{
   Ast_Type_Kind kind;
   S32 size;
   S32 align;
   S32 is_unsigned;
   S32 type_id;
+  S32 padding;
 
   Ast *ast;
   union{
@@ -137,7 +138,7 @@ const SizeU pointer_align = __alignof(SizeU);
 global Ast_Type type__void = {TYPE_VOID};
 global Ast_Type type__string = {TYPE_STRING, sizeof(String), __alignof(String)};
 global Ast_Type type__bool = {TYPE_BOOL, sizeof(bool), __alignof(bool)};
-global Ast_Type type__type = {TYPE_TYPE};
+global Ast_Type type__type = {TYPE_TYPE, sizeof(U32), __alignof(U32)};
 
 global Ast_Type type__f32 = {TYPE_F32, sizeof(F32), __alignof(F32)};
 global Ast_Type type__f64 = {TYPE_F64, sizeof(F64), __alignof(F64)};
diff --git a/examples/drawing_to_screen_using_windows_api.kl b/examples/drawing_to_screen_using_windows_api.kl
index 42b9999..302d57a 100644
--- a/examples/drawing_to_screen_using_windows_api.kl
+++ b/examples/drawing_to_screen_using_windows_api.kl
@@ -24,9 +24,11 @@ CreateBitmap :: (size: Vec2I, bottom_up: Bool = true): Windows_Bitmap
   if bottom_up == false
     result.size.y = -result.size.y
 
+  header_size: U32 = SizeOf(BITMAPINFOHEADER)
+  Assert(header_size == 40)
   bminfo := BITMAPINFO{
     BITMAPINFOHEADER{
-      biSize          = 40, // @todo!!! SizeOf(BITMAPINFOHEADER),
+      biSize          = header_size,
       biWidth         = size.x->LONG,
       biHeight        = size.y->LONG,
       biPlanes        = 1,