diff --git a/nac3core/src/toplevel/composer.rs b/nac3core/src/toplevel/composer.rs
index 9dd980d2..5819be38 100644
--- a/nac3core/src/toplevel/composer.rs
+++ b/nac3core/src/toplevel/composer.rs
@@ -1169,20 +1169,20 @@ impl TopLevelComposer {
                 methods,
                 fields,
                 type_vars,
-                name,
+                name: class_name,
                 object_id,
                 resolver: _,
                 ..
             } = &*class_def
             {
-                let mut has_init = false;
+                let mut init_id: Option<DefinitionId> = None;
                 // get the class contructor type correct
                 let (contor_args, contor_type_vars) = {
                     let mut constructor_args: Vec<FuncArg> = Vec::new();
                     let mut type_vars: HashMap<u32, Type> = HashMap::new();
-                    for (name, func_sig, ..) in methods {
+                    for (name, func_sig, id) in methods {
                         if name == "__init__" {
-                            has_init = true;
+                            init_id = Some(*id);
                             if let TypeEnum::TFunc(sig) = self.unifier.get_ty(*func_sig).as_ref() {
                                 let FunSignature { args, vars, .. } = &*sig.borrow();
                                 constructor_args.extend_from_slice(args);
@@ -1207,11 +1207,22 @@ impl TopLevelComposer {
                 self.unifier.unify(constructor.unwrap(), contor_type)?;
 
                 // class field instantiation check
-                // TODO: this is a really simple one, more check later
-                if !has_init && !fields.is_empty() {
-                    return Err(format!("fields of class {} not fully initialized", name))
+                if let (Some(init_id), false) = (init_id, fields.is_empty()) {
+                    let init_ast =
+                        self.definition_ast_list.get(init_id.0).unwrap().1.as_ref().unwrap();
+                    if let ast::StmtKind::FunctionDef { name, body, .. } = &init_ast.node {
+                        if name != "__init__" {
+                            unreachable!("must be init function here")
+                        }
+                        let all_inited = Self::get_all_assigned_field(body.as_slice())?;
+                        if fields.iter().any(|(x, _)| !all_inited.contains(x)) {
+                            return Err(format!(
+                                "fields of class {} not fully initialized",
+                                class_name
+                            ));
+                        }
+                    }
                 }
-
             }
         }
 
diff --git a/nac3core/src/toplevel/helper.rs b/nac3core/src/toplevel/helper.rs
index 114c345d..c024631c 100644
--- a/nac3core/src/toplevel/helper.rs
+++ b/nac3core/src/toplevel/helper.rs
@@ -268,4 +268,73 @@ impl TopLevelComposer {
             unifier,
         )
     }
+
+    pub fn get_all_assigned_field(stmts: &[ast::Stmt<()>]) -> Result<HashSet<String>, String> {
+        let mut result: HashSet<String> = HashSet::new();
+        for s in stmts {
+            match &s.node {
+                ast::StmtKind::AnnAssign { target, .. }
+                    if {
+                        if let ast::ExprKind::Attribute { value, .. } = &target.node {
+                            if let ast::ExprKind::Name { id, .. } = &value.node {
+                                id == "self"
+                            } else {
+                                false
+                            }
+                        } else {
+                            false
+                        }
+                    } =>
+                {
+                    return Err(format!(
+                        "redundant type annotation for class fields at {}",
+                        s.location
+                    ))
+                }
+                ast::StmtKind::Assign { targets, .. } => {
+                    for t in targets {
+                        if let ast::ExprKind::Attribute { value, attr, .. } = &t.node {
+                            if let ast::ExprKind::Name { id, .. } = &value.node {
+                                if id == "self" {
+                                    result.insert(attr.clone());
+                                }
+                            }
+                        }
+                    }
+                }
+                // TODO: do not check for For and While?
+                ast::StmtKind::For { body, orelse, .. }
+                | ast::StmtKind::While { body, orelse, .. } => {
+                    result.extend(Self::get_all_assigned_field(body.as_slice())?);
+                    result.extend(Self::get_all_assigned_field(orelse.as_slice())?);
+                }
+                ast::StmtKind::If { body, orelse, .. } => {
+                    let inited_for_sure = Self::get_all_assigned_field(body.as_slice())?
+                        .intersection(&Self::get_all_assigned_field(orelse.as_slice())?)
+                        .cloned()
+                        .collect::<HashSet<String>>();
+                    result.extend(inited_for_sure);
+                }
+                ast::StmtKind::Try { body, orelse, finalbody, .. } => {
+                    let inited_for_sure = Self::get_all_assigned_field(body.as_slice())?
+                        .intersection(&Self::get_all_assigned_field(orelse.as_slice())?)
+                        .cloned()
+                        .collect::<HashSet<String>>();
+                    result.extend(inited_for_sure);
+                    result.extend(Self::get_all_assigned_field(finalbody.as_slice())?);
+                }
+                ast::StmtKind::With { body, .. } => {
+                    result.extend(Self::get_all_assigned_field(body.as_slice())?);
+                }
+                ast::StmtKind::Pass => {}
+                ast::StmtKind::Assert { .. } => {}
+                ast::StmtKind::Expr { .. } => {}
+
+                _ => {
+                    unimplemented!()
+                }
+            }
+        }
+        Ok(result)
+    }
 }
diff --git a/nac3core/src/toplevel/test.rs b/nac3core/src/toplevel/test.rs
index 730e9344..54893d36 100644
--- a/nac3core/src/toplevel/test.rs
+++ b/nac3core/src/toplevel/test.rs
@@ -870,7 +870,7 @@ fn test_analyze(source: Vec<&str>, res: Vec<&str>) {
                     return SELF
                 def sum(self) -> int32:
                     if self.a == 0:
-                        return self.a + self
+                        return self.a
                     else:
                         a = self.a
                         self.a = self.a - 1
@@ -898,7 +898,7 @@ fn test_analyze(source: Vec<&str>, res: Vec<&str>) {
                 return ret * ret
         "},
         indoc! {"
-            def sum3(l: list[V]) -> V:
+            def sum_three(l: list[V]) -> V:
                 return l[0] + l[1] + l[2]
         "},
         indoc! {"
@@ -921,7 +921,11 @@ fn test_analyze(source: Vec<&str>, res: Vec<&str>) {
                 b: bool
                 def __init__(self, aa: G):
                     self.a = aa
-                    self.b = True
+                    if 2 > 1:
+                        self.b = True
+                    else:
+                        # self.b = False
+                        pass
                 def fun(self, a: G) -> list[G]:
                     ret = [a, self.a]
                     return ret if self.b else self.fun(self.a)
@@ -930,6 +934,30 @@ fn test_analyze(source: Vec<&str>, res: Vec<&str>) {
     vec![];
     "type var class"
 )]
+#[test_case(
+    vec![
+        indoc! {"
+            class A:
+                def fun(self):
+                    1 + 2
+        "},
+        indoc!{"
+            class B:
+                a: int32
+                b: bool
+                def __init__(self):
+                    # self.b = False
+                    if 3 > 2:
+                        self.a = 3
+                        self.b = False
+                    else:
+                        self.a = 4
+                        self.b = True
+        "}
+    ],
+    vec![];
+    "no_init_inst_check"
+)]
 fn test_inference(source: Vec<&str>, res: Vec<&str>) {
     let print = true;
     let mut composer: TopLevelComposer = Default::default();