diff --git a/crates/erg_compiler/context/inquire.rs b/crates/erg_compiler/context/inquire.rs
index 6e1f93bf..163b6d43 100644
--- a/crates/erg_compiler/context/inquire.rs
+++ b/crates/erg_compiler/context/inquire.rs
@@ -458,6 +458,10 @@ impl Context {
         }
         match self.get_attr_from_nominal_t(obj, ident, input, namespace) {
             Ok(vi) => {
+                if let Some(self_t) = vi.t.self_t() {
+                    self.sub_unify(obj.ref_t(), self_t, obj.loc(), Some(&"self".into()))
+                        .map_err(|mut e| e.remove(0))?;
+                }
                 return Ok(vi);
             }
             Err(e) if e.core.kind == ErrorKind::AttributeError => {}
diff --git a/crates/erg_compiler/ty/mod.rs b/crates/erg_compiler/ty/mod.rs
index 1d428262..cb525ec7 100644
--- a/crates/erg_compiler/ty/mod.rs
+++ b/crates/erg_compiler/ty/mod.rs
@@ -360,6 +360,10 @@ impl SubrType {
         })
     }
 
+    pub fn is_method(&self) -> bool {
+        self.self_t().is_some()
+    }
+
     pub fn non_var_params(&self) -> impl Iterator<Item = &ParamTy> + Clone {
         if self.var_params.is_some() {
             self.non_default_params.iter().chain([].iter())
@@ -1268,6 +1272,16 @@ impl Type {
         }
     }
 
+    pub fn is_method(&self) -> bool {
+        match self {
+            Self::FreeVar(fv) if fv.is_linked() => fv.crack().is_method(),
+            Self::Refinement(refine) => refine.t.is_method(),
+            Self::Subr(subr) => subr.is_method(),
+            Self::Quantified(quant) => quant.is_method(),
+            _ => false,
+        }
+    }
+
     pub fn is_quantified(&self) -> bool {
         match self {
             Self::FreeVar(fv) if fv.is_linked() => fv.crack().is_quantified(),
diff --git a/crates/erg_compiler/ty/typaram.rs b/crates/erg_compiler/ty/typaram.rs
index a668375f..7ba2a141 100644
--- a/crates/erg_compiler/ty/typaram.rs
+++ b/crates/erg_compiler/ty/typaram.rs
@@ -720,7 +720,11 @@ impl TyParam {
     pub fn qvars(&self) -> Set<(Str, Constraint)> {
         match self {
             Self::FreeVar(fv) if !fv.constraint_is_uninited() => {
-                set! { (fv.unbound_name().unwrap(), fv.constraint().unwrap()) }
+                if let (Some(name), Some(constraint)) = (fv.unbound_name(), fv.constraint()) {
+                    set! { (name, constraint) }
+                } else {
+                    set! {}
+                }
             }
             Self::FreeVar(fv) if fv.is_linked() => fv.forced_as_ref().linked().unwrap().qvars(),
             Self::Type(t) => t.qvars(),
diff --git a/tests/should_err/move.er b/tests/should_err/move.er
new file mode 100644
index 00000000..c98240ca
--- /dev/null
+++ b/tests/should_err/move.er
@@ -0,0 +1,6 @@
+a = ![]
+
+a.sort! # WARN
+
+# NOTE: For safety reasons this is assumed to be an error, but maybe this restriction can be relaxed
+print! a # ERR
diff --git a/tests/test.rs b/tests/test.rs
index 941e5310..1f19d065 100644
--- a/tests/test.rs
+++ b/tests/test.rs
@@ -249,3 +249,8 @@ fn exec_var_args() -> Result<(), ()> {
 fn exec_var_args_err() -> Result<(), ()> {
     expect_failure("tests/should_err/var_args.er", 2)
 }
+
+#[test]
+fn exec_move() -> Result<(), ()> {
+    expect_failure("tests/should_err/move.er", 1)
+}